EVALUATION OF UNKNOWN PRIMARY (CARCINOMA OF UNKNOWN PRIMARY - CUP) IN HEAD AND NECK

(50 Marks - RGUHS Standard)

1. DEFINITION

"The presentation of biopsy-proven squamous cell carcinoma in one or more cervical lymph nodes in the absence of an obvious primary tumour despite rigorous clinical examination, appropriate cross-sectional imaging and examination under anaesthesia including ipsilateral tonsillectomy and biopsy of tongue base mucosa (+/- biopsy of post-nasal space and/or ipsilateral piriform fossa)."

• Scott-Brown's Otorhinolaryngology, Head & Neck Surgery, Chapter 17 (Simo, Jeannon, Guerrero Urbano)

• Synonyms: Carcinoma of Occult Primary (COP), Squamous Cell Carcinoma of Unknown Primary (SCCUP)
• Represents: 1-3% of all head and neck squamous cell carcinomas
• Cummings Otolaryngology, Chapter on Unknown Primary

2. HISTORICAL BACKGROUND

┌─────────────────────────────────────────────────────────────────────┐
│                    HISTORICAL MILESTONES                            │
├─────────────┬───────────────────────────────────────────────────────┤
│ 1882        │ Volkmann's "Branchiogenic cyst degeneration" theory    │
│ 1940        │ Martin & Morfit dismiss branchiogenic theory (only     │
│             │ 8/55 patients met criteria)                           │
│ 1950        │ Hayes Martin establishes criteria for Branchiogenic Ca │
│ 1963        │ France & Lucas - first management guidelines           │
│ 1966        │ Jesse & Neff - landmark series on metastatic cervical  │
│             │ nodes with unknown primary                            │
│ 2011        │ Karni et al. - TLM paradigm for unknown primary        │
│ 2015+       │ TORS era with >80% detection rates                    │
│ 2020        │ ASCO Guidelines for SCCUP                             │
└─────────────┴───────────────────────────────────────────────────────┘

1. Cervical cyst in the line of the branchial apparatus
2. Histology consistent with origin from branchial vestige
3. No primary site found after 5 years follow-up
4. Metastases only along distribution of branchial derivation

3. PATHOPHYSIOLOGY / HYPOTHESES

┌──────────────────────────────────────────────────────────────────┐
│              TWO COMPETING HYPOTHESES FOR CUP                    │
├──────────────────────┬───────────────────────────────────────────┤
│  HYPOTHESIS 1        │  HYPOTHESIS 2                             │
│  "Small Primary"     │  "Regressed Primary"                      │
│                      │                                           │
│  A small primary     │  The primary tumour undergoes             │
│  exists but is       │  spontaneous immune-mediated              │
│  below detection     │  regression after seeding the            │
│  threshold           │  metastatic node                         │
│                      │                                           │
│  Evidence: ~50% of   │  Evidence: Some CUP patients             │
│  CUP cases have      │  have brisk lymphocytic response          │
│  primary found on    │  in nodes suggesting immune              │
│  TORS/TLM            │  clearance of primary                    │
└──────────────────────┴───────────────────────────────────────────┘

• HPV oncogenesis: The increasing incidence of HPV-positive oropharyngeal SCC is the most common context for CUP in the modern era. HPV-16/18 drives malignant transformation in tonsillar crypts where small tumours can metastasize early before becoming clinically apparent.

4. INCIDENCE AND EPIDEMIOLOGY

5. SITES OF POSSIBLE PRIMARY - ANATOMICAL BASIS

┌──────────────────────────────────────────────────────────────────────────┐
│           CERVICAL NODE LEVEL → LIKELY PRIMARY SITE                     │
├────────────────┬─────────────────────────────────────────────────────────┤
│  Level I       │  Oral cavity (floor of mouth, lips, anterior tongue)    │
│  Level II      │  Oropharynx (tonsil, tongue base, soft palate),         │
│  (most common) │  Nasopharynx, Larynx, Hypopharynx                       │
│  Level III     │  Oropharynx, Hypopharynx, Larynx                        │
│  Level IV      │  Hypopharynx, Larynx, Oesophagus, Thyroid              │
│  Level V       │  Nasopharynx, Thyroid, skin of scalp/posterior neck     │
│  Posterior     │  Nasopharynx (EBV-associated)                           │
│  triangle      │                                                          │
└────────────────┴─────────────────────────────────────────────────────────┘

• Palatine tonsils - Most common (~40%)
• Lingual tonsil (tongue base) - Second most common (~30%)
• Nasopharynx - Especially EBV-associated
• Soft palate, posterior pharyngeal wall

6. CLINICAL FEATURES

Presentation:

• Painless neck mass - Most common (>90%)
• Usually lateral neck - Level II most frequent
• May be cystic (mimicking branchial cyst) - IMPORTANT: all cystic lateral neck masses in patients >35 years must be considered malignant until proven otherwise (Scott-Brown's)
• Size: typically >2 cm at presentation
• Hard, firm, may be fixed in advanced cases
• Bilateral nodes in ~10% of cases

RED FLAG FEATURES suggesting occult primary:

• Unilateral cervical lymphadenopathy in adult >35 years
• Node >2 cm, hard, non-tender
• Rapid growth
• Cystic node in posterior triangle

7. DIFFERENTIAL DIAGNOSIS OF NECK MASS

                    NECK MASS IN ADULT
                          |
         ┌────────────────┼────────────────┐
      Inflammatory    Neoplastic        Congenital
      (Reactive)      (Primary/         (Branchial cyst,
                      Secondary)        Thyroglossal)
                          |
                ┌─────────┴─────────┐
             Primary           Secondary
             (Salivary,         (Metastatic)
              Lymphoma)              |
                              ┌──────┴──────┐
                           Known         UNKNOWN
                           Primary       PRIMARY (CUP)

8. EVALUATION AND DIAGNOSIS - STEP-BY-STEP PROTOCOL

STEP 1: HISTORY TAKING

• Duration, rate of growth of neck mass
• Previous head & neck surgeries (tonsillectomy, dental extractions)
• Smoking and alcohol history (increased risk of all H&N SCC sites)
• HPV exposure risk factors
• Symptoms: dysphagia, hoarseness, otalgia, epistaxis, nasal obstruction
• Weight loss, fatigue (systemic metastases)

STEP 2: CLINICAL EXAMINATION (Systematic)

┌──────────────────────────────────────────────────────────────────┐
│              SYSTEMATIC CLINICAL EXAMINATION                     │
├─────────────────────────────────────────────────────────────────┤
│  SKIN: Scalp, face, pinna - for melanoma, SCC                   │
│  ORAL CAVITY: Lips, gingiva, buccal mucosa, hard palate,         │
│               floor of mouth, anterior 2/3 tongue               │
│  OROPHARYNX: Tonsils (size, ulceration, asymmetry),             │
│              Tongue base (palpation essential),                  │
│              Soft palate, posterior pharyngeal wall              │
│  NASOPHARYNX: Posterior rhinoscopy / nasal endoscopy            │
│  HYPOPHARYNX: Indirect laryngoscopy / flexible endoscopy        │
│  LARYNX: Mobility of cords                                       │
│  THYROID: Palpation                                              │
│  NECK: Size, consistency, mobility, level of nodes              │
│  SALIVARY GLANDS: Parotid, submandibular                        │
└──────────────────────────────────────────────────────────────────┘

9. INVESTIGATIONS

FLOW CHART - DIAGNOSTIC ALGORITHM

                    NECK MASS WITH SUSPECTED MALIGNANCY
                               │
                               ▼
                    ┌──────────────────────┐
                    │  CLINICAL EXAMINATION│
                    │  + FNL ± NBI         │
                    └──────────┬───────────┘
                               │ No primary found
                               ▼
                    ┌──────────────────────┐
                    │  FNAC OF NECK MASS   │◄── Core needle biopsy
                    │  (First line         │    if FNAC inconclusive
                    │   investigation)     │
                    └──────────┬───────────┘
                               │ SCC confirmed
                               ▼
                    ┌──────────────────────┐
                    │  SEND FOR:           │
                    │  • p16 IHC (HPV)     │
                    │  • EBV ISH/serology  │
                    └──────────┬───────────┘
                               │
               ┌───────────────┼────────────────┐
               ▼               ▼                ▼
         p16 POSITIVE    EBV POSITIVE      p16/EBV NEGATIVE
         (HPV-related)   (NPC likely)      (Unknown aetiology)
               │               │                │
               ▼               ▼                ▼
         Primary likely   Nasopharynx      Broader search
         in Oropharynx   (MRI/biopsy)      needed
               │
               ▼
         CROSS-SECTIONAL IMAGING
         ┌─────────────┬──────────────┐
         │  CT NECK    │   MRI NECK   │
         │  with       │   (Superior  │
         │  contrast   │   for tongue │
         │             │   base, NP)  │
         └─────────────┴──────────────┘
               │ Still no primary
               ▼
         ┌──────────────────────┐
         │   PET-CT (FDG)       │◄── Detection rate 24-37%
         │   (Whole body +      │    False positive rate in
         │   head & neck)       │    tonsils 15-39%
         └──────────┬───────────┘
               │ Still no primary
               ▼
         ┌──────────────────────────────────────────┐
         │   PANENDOSCOPY UNDER GENERAL ANAESTHESIA  │
         │                                          │
         │   TRIPLE ENDOSCOPY:                      │
         │   • Laryngoscopy                         │
         │   • Pharyngoscopy (including NBI)        │
         │   • Oesophagoscopy                       │
         │   • Bronchoscopy (if indicated)          │
         │                                          │
         │   + Biopsies:                            │
         │   • Nasopharynx (telescope-guided)       │
         │   • Ipsilateral palatine TONSILLECTOMY   │
         │   • Tongue base biopsy / mucosectomy     │
         │   • Piriform sinus biopsy                │
         └──────────┬───────────────────────────────┘
               │ Still no primary found
               ▼
         ┌──────────────────────────────────────────┐
         │  TRANSORAL ROBOTIC/LASER SURGERY (TORS/  │
         │  TLM):                                   │
         │  • Lingual tonsillectomy                 │
         │  • Bilateral palatine tonsillectomy      │
         │  • "Cut-surface view" biopsies (TLM)     │
         │  Detection rate: 60-94%                  │
         └──────────┬───────────────────────────────┘
               │ Primary identified → treat accordingly
               │ Primary NOT identified
               ▼
         ┌──────────────────────────────────────────┐
         │         TRUE CUP MANAGEMENT              │
         │  Neck dissection + Radiation to neck     │
         │  +/- mucosal irradiation                 │
         └──────────────────────────────────────────┘

10. INVESTIGATIONS IN DETAIL

A. FINE NEEDLE ASPIRATION CYTOLOGY (FNAC)

• First line investigation for all neck masses
• Do NOT perform open excision biopsy first - this disrupts tissue planes and adversely affects prognosis and subsequent management
• Sensitivity ~85-90% for malignancy
• Caveat: FNAC showing "no malignant cells" in a suspicious neck mass does not exclude CUP - proceed with core needle biopsy or excision biopsy only as LAST resort

B. CORE NEEDLE BIOPSY

• Provides histological core (not just cytology)
• Allows IHC testing: p16, EBV ISH, cytokeratins
• Preferred over open biopsy

C. IHC AND MOLECULAR MARKERS ON BIOPSY

┌─────────────────────────────────────────────────────────────────┐
│                BIOMARKER PANEL ON NECK BIOPSY                   │
├─────────────────┬───────────────────────────────────────────────┤
│  p16 IHC        │  HPV-related OPC marker; strong diffuse        │
│                 │  positivity (>70% cells) = HPV-related         │
│  EBV ISH/EBER   │  Nasopharyngeal carcinoma marker              │
│  HPV DNA ISH    │  Confirms high-risk HPV types 16, 18          │
│  CK5/6, p40     │  Squamous differentiation markers             │
│  CK7, CK20      │  Adenocarcinoma lineage differentiation       │
│  TTF-1          │  Lung or thyroid origin                       │
│  PSA            │  Prostate primary                              │
│  ER/PR          │  Breast primary                                │
└─────────────────┴───────────────────────────────────────────────┘

• p16+HPV ISH positive → Highly predictive of oropharyngeal origin → direct TORS/TLM to tonsil/tongue base (Cummings, Chapter 96)
• EBV positive → Nasopharyngeal classification applied; AJCC EBV-associated NPC staging used (Scott-Brown's)

D. IMAGING

i. CT Neck with Contrast

• First-line cross-sectional imaging
• Identifies: node levels, extranodal extension, vascular involvement, suspicious mucosal thickening
• Detection of primary: ~25-35%

ii. MRI Neck

• Superior for: tongue base, nasopharynx, parapharyngeal space, skull base
• Best for EBV-associated nasopharyngeal tumours
• Better soft tissue delineation

iii. PET-CT (FDG-PET)

• Detection rate for unknown primary: 24-37% (Cummings, Chapter 96)
• False positive rates in tonsils: 15-39% - major limitation
• Advantages:
  • Whole body staging (detects synchronous primaries, distant mets)
  • Guides biopsy sites
  • Higher sensitivity than CT/MRI alone
• NICE recommendations (Scott-Brown's): PET-CT should be performed early in the investigation pathway

       PET-CT DETECTION RATES IN CUP
       (Meta-analysis by Rusthoven et al.)
       
       Overall detection rate:    ~37%
       Sensitivity:               ~88%
       Specificity:               ~75%
       Change in management:      ~25% of cases

iv. Ultrasound-guided FNAC

• For laterality and level assessment
• Better sensitivity than blind FNAC for deep nodes

E. EXAMINATION UNDER ANAESTHESIA (EUA) + PANENDOSCOPY

┌──────────────────────────────────────────────────────────────────┐
│              PANENDOSCOPY PROTOCOL                               │
├──────────────────────────────────────────────────────────────────┤
│ Step 1: Laryngoscopy                                             │
│         - Direct + microscope-assisted                           │
│         - Assess glottis, subglottis, arytenoids, pyriform sinus │
│                                                                  │
│ Step 2: Pharyngoscopy                                            │
│         - Nasopharyngoscopy with rigid telescope                 │
│         - Assessment under high magnification (NBI useful)       │
│                                                                  │
│ Step 3: Oesophagoscopy                                           │
│         - Rule out postcricoid/upper oesophageal primary        │
│                                                                  │
│ Step 4: Bronchoscopy (selective)                                 │
│         - Only if respiratory symptoms or Level IV nodes        │
│                                                                  │
│ BIOPSIES TAKEN:                                                  │
│ • Nasopharynx - telescope-guided (NOT blind)                    │
│ • Palatine tonsillectomy (IPSILATERAL ± bilateral)              │
│ • Tongue base mucosectomy / biopsy                              │
│ • Piriform sinus (ipsilateral)                                   │
│ • Any suspicious mucosal lesion                                  │
└──────────────────────────────────────────────────────────────────┘

Nasopharyngeal Biopsy Guidelines (Scott-Brown's):

• Blind biopsies are unsatisfactory - poor yield
• Must be guided by rigid telescopes
• Only perform when imaging shows abnormality in NP

Tonsillectomy (Scott-Brown's, Chapter 17):

• Ipsilateral tonsillectomy is standard
• Bilateral tonsillectomy indicated because:
  • Primary resides in contralateral tonsil in up to 10% of cases
  • HPV-related tumours can be multifocal
  • Reduces need for bilateral irradiation
  • Tonsillar remnants (post-prior tonsillectomy) must also be excised

11. TRANSORAL APPROACHES - THE MODERN PARADIGM

Transoral Laser Microsurgery (TLM) - Karni Protocol (2011)

┌──────────────────────────────────────────────────────────────────┐
│         TLM PROTOCOL FOR UNKNOWN PRIMARY (Karni et al.)          │
├──────────────────────────────────────────────────────────────────┤
│ Step 1: Naked-eye laryngoscopy of all at-risk mucosal surfaces   │
│ Step 2: Manual palpation of oropharyngeal surfaces               │
│ Step 3: Microscope/rod telescope examination - look for:         │
│         • Pallor, hypervascularity                               │
│         • Palisading/corkscrew telangiectatic microcirculation   │
│         • Papillary growth features                              │
│         • Slight mucosal prominence/raised lesions               │
│         • Superficial firmness, mucosal friability               │
│ Step 4: CO2 laser directed biopsies (3-5mm cut)                  │
│         → "Cut-surface view" of submucosa                        │
│         → Frozen section analysis                                │
│ Step 5: If no primary found → formal lingual tonsillectomy       │
│         + ipsilateral palatine tonsillectomy                     │
│ Step 6: If still negative → ± contralateral tonsillectomy/        │
│         nasopharyngeal biopsies                                  │
│                                                                  │
│ RESULT: Detection rate improved from 25% → 94%                  │
└──────────────────────────────────────────────────────────────────┘

Transoral Robotic Surgery (TORS)

COMPARISON OF TRANSORAL APPROACHES (Meta-analysis, Al-Lami et al. 2022, PMID 35144209):

Total patients in meta-analysis: 777
Overall primary identification: 567/777 = 64% (pooled)

By technique:
┌───────────────────────────┬──────────────────────────────────────┐
│ Lingual tonsillectomy     │ 45% (n=273 patients)                │
│ Palatine tonsillectomy    │ 32% (n=118 patients)                │
│ TORS                      │ 60% (95% CI: 49-70%)                │
│ TLM                       │ 80% (95% CI: 58-101%)               │
│ TOEC (electrocautery)     │ 41% (95% CI: 5-76%)                 │
└───────────────────────────┴──────────────────────────────────────┘

HPV-positive tumours: 529/777 (68%)
Detection rates by HPV status:
  HPV+ tumours: 178/216 = 82%
  HPV- tumours:   7/59 = 12%

12. STAGING (AJCC/UICC 8th Edition)

Key changes in 8th edition (Scott-Brown's, Chapter on TNM Staging):

CURRENT STAGING OF CUP (AJCC 8th Edition, 2017):

1. T0 category ELIMINATED except for:
   - EBV-associated nasopharyngeal carcinoma (T0N+)
   - HPV/p16-positive oropharyngeal carcinoma (T0N+)
   - Salivary gland cancers

2. If no primary identified → node may originate from ANY mucosal site
   → No rationale for T0 outside virally-associated cancers

3. SEPARATE STAGING SYSTEMS for:
   a) p16+ (HPV) oropharyngeal CUP → use OPC p16+ staging
   b) EBV-associated CUP → use NPC staging
   c) Others → staging based on nodal status (pN, cN)

13. MANAGEMENT - COMPREHENSIVE FLOW CHART

                     CONFIRMED CUP (SCC in Cervical Node)
                                    │
                    ┌───────────────┴────────────────┐
             PRIMARY FOUND                    PRIMARY NOT FOUND
             (via TORS/TLM)                  (True CUP)
                    │                                │
         ┌──────────┴──────────┐         ┌──────────┴──────────┐
      SURGICAL                NON-SX    N1-N2a               N2b-N3
      CANDIDATE               CANDIDATE  No ENE               Or ENE+
         │                       │         │                     │
    TORS resection +         CRT or RT   Selective            Modified
    Neck dissection          alone       Neck Dissection      Radical ND
         │                               ± PORT                + CRT
    Neck dissection:
    • N1: SND (I-III)
    • N2: MRND (I-V)
    • N3/ENE: +/- RT

         ┌─────────────────────────────────────────────────┐
         │             RADIATION THERAPY                   │
         │                                                  │
         │  UNILATERAL RT: neck + ipsilateral mucosa       │
         │  Indication: p16+, N1-2, no ENE, low risk       │
         │                                                  │
         │  BILATERAL "TOTAL MUCOSAL IRRADIATION":          │
         │  Indication: p16-, N2c-N3, ENE+, high risk      │
         │  Fields: bilateral neck + pharyngeal axis        │
         │  (nasopharynx to postcricoid) 50-70 Gy           │
         │                                                  │
         │  IMRT (preferred over conventional RT):          │
         │  • Parotid sparing → reduces xerostomia         │
         │  • Better mucosal coverage                       │
         │  • Grade ≥3 xerostomia: 5-36% at 6 months      │
         │  • Feeding tube dependence: 0-5% at 12 months   │
         └─────────────────────────────────────────────────┘

RECOMMENDED TREATMENT PROTOCOLS (Scott-Brown's, Chapter 17):

• Single modality: Selective neck dissection OR involved-field RT alone
• If treated surgically: careful mucosal surveillance during follow-up

• Combined modality: Surgery (MRND) + postoperative RT
• ENE+ or positive margins: add concurrent chemotherapy (cisplatin)

• Concurrent cisplatin with RT for ENE+, positive margins, or advanced nodal disease
• Cetuximab (anti-EGFR) as alternative to cisplatin in cisplatin-ineligible patients
• Pembrolizumab (PD-1 inhibitor): Emerging role in CUP (Frontiers in Oncology, Kalavacherla et al. 2022, PMID 36185196)

14. PROGNOSIS AND TREATMENT OUTCOMES

┌─────────────────────────────────────────────────────────────────┐
│                   PROGNOSTIC FACTORS IN CUP                     │
├──────────────────────┬──────────────────────────────────────────┤
│  FAVORABLE           │  UNFAVORABLE                             │
├──────────────────────┼──────────────────────────────────────────┤
│  p16/HPV positive    │  p16/HPV negative                        │
│  N1 disease          │  N3 disease                              │
│  No ENE              │  ENE present                             │
│  Single node         │  Multiple bilateral nodes                │
│  Age <55 years       │  Age >55 years (old criteria was 45)     │
│  No smoking history  │  Smoking + alcohol history               │
│  Primary identified  │  Primary never found                     │
│  Complete resection  │  Incomplete surgery                      │
└──────────────────────┴──────────────────────────────────────────┘

• Overall CUP: ~50% (historical)
• HPV+ CUP: ~75-80%
• HPV- CUP: ~30-40%
• N1 without ENE: ~70%
• N3 with ENE: ~20-30%

• Locoregional: Most common (~40%)
• Distant metastases: Lung, liver, bone (~25-30%)
• Subsequent primary emergence: 5-25% (most in oropharynx)

15. NECK DISSECTION IN CUP

┌──────────────────────────────────────────────────────────────┐
│           NECK DISSECTION TYPES IN CUP                       │
├──────────────────────────────────────────────────────────────┤
│  Selective ND (SND I-III):                                   │
│  → N1 disease, no ENE, p16+ HPV-related CUP                 │
│                                                              │
│  Selective ND (I-IV or II-IV):                               │
│  → Depending on nodal levels involved                        │
│                                                              │
│  Modified Radical ND (MRND, types I-III):                    │
│  → N2-N3 disease                                             │
│  → Preserve: Internal jugular vein, SCM, XI nerve (as many  │
│    as possible while achieving oncological clearance)        │
│                                                              │
│  Radical ND:                                                 │
│  → When adherent to major vessels/SCM/XI nerve               │
│  → N3 with ENE                                               │
│                                                              │
│  IMPORTANT: Diagnostic node biopsy BEFORE definitive         │
│  treatment is DETRIMENTAL - increases recurrence (McGuirt     │
│  & McCabe 1978; Razack et al. 1977)                          │
└──────────────────────────────────────────────────────────────┘

16. NICE RECOMMENDATIONS (UK - quoted in Scott-Brown's)

1. All adults >35 years with lateral cystic neck mass → enter CUP investigation protocol
2. FNL with NBI should be performed in the outpatient clinic
3. Cross-sectional imaging (CT ± MRI) followed by PET-CT
4. Panendoscopy with ipsilateral tonsillectomy + tongue base biopsy
5. If primary not found after above → TORS/TLM bilateral tonsillectomy and lingual tonsillectomy
6. p16 and EBV testing mandatory on all biopsy material
7. IMRT preferred for mucosal irradiation (parotid-sparing)

17. RECENT ADVANCES (2021-2026)

A. Transoral Robotic Surgery (TORS)

• Detection rates 60-80% in HPV+ patients
• Combined TORS palatine + lingual tonsillectomy achieves 82% detection in HPV+ CUP
• Allows simultaneous diagnostic + therapeutic resection with intraoperative frozen section

B. Narrow Band Imaging (NBI)

• Used during flexible endoscopy and panendoscopy
• Highlights neovascularization (brown submucosal capillaries at 415 nm, cyan deeper vessels at 540 nm)
• Meta-analysis: Sensitivity 74.1%, Specificity 94.1% (Chabrillac et al., Eur Ann ORL 2021, PMID 33722467)

C. HPV/p16 Guided De-escalation

• HPV+ SCCUP has dramatically better prognosis
• Trials underway to de-escalate RT (lower dose, smaller fields) in HPV+ CUP
• Potential to reduce xerostomia, dysphagia, feeding tube dependence (Kalavacherla et al. Front Oncol 2022, PMID 36185196)

D. IMRT and Proton Beam Therapy

• IMRT: Standard of care; reduces xerostomia rates to 5-36% at 6 months (vs. >50% conventional RT)
• Feeding tube dependence: 0-5% at 12 months with IMRT
• Proton beam therapy: investigational; further reduces dose to salivary glands and pharyngeal muscles

E. Immunotherapy

• Pembrolizumab (PD-1 inhibitor): Demonstrated efficacy in CUP cases with PD-L1 expression
• Nivolumab: Under investigation for recurrent/metastatic CUP
• Tumor mutational burden (TMB) as biomarker for immunotherapy response

F. Liquid Biopsy / ctDNA

• Circulating tumor DNA (ctDNA) to identify primary site or monitor response
• Early data: ctDNA analysis may detect primary site-specific mutations (e.g., KEAP1/KRAS for lung, PIK3CA for HPV-related OPC)
• Cancer Research 2017; Clin Cancer Res 2021 - cited in Harrison's 22nd Edition

G. Gene Expression Profiling

• CancerTYPE ID, Rosetta Cancer Origin - molecular tests analyzing mRNA expression patterns
• Can predict tissue of origin with ~80% accuracy in adenocarcinoma CUP
• Limited data for H&N SCC CUP specifically

H. Next-Generation Sequencing (NGS) / Comprehensive Genomic Profiling

• Identifies actionable mutations irrespective of primary site
• NCCN guidelines recommend NGS for CUP patients to identify targeted therapy options
• TMB-high → immunotherapy
• HER2 amplification → trastuzumab
• NTRK fusion → larotrectinib

18. RGUHS EXAM FORMAT - MARKS DISTRIBUTION SUGGESTION

19. SUMMARY DIAGRAM

┌────────────────────────────────────────────────────────────────────────────┐
│                  CUP IN HEAD & NECK - MASTER SUMMARY                       │
├────────────────────────────────────────────────────────────────────────────┤
│                                                                            │
│  PRESENTATION: Adult, painless cervical lymphadenopathy, cystic node      │
│                                                                            │
│  INVESTIGATION HIERARCHY:                                                  │
│  1. FNL + NBI (clinic) → FNAC/Core biopsy → p16 + EBV testing            │
│  2. CT neck with contrast → MRI (if required)                             │
│  3. PET-CT (whole body)                                                    │
│  4. Panendoscopy + Ipsilateral tonsillectomy + Tongue base biopsy         │
│  5. TORS/TLM (bilateral tonsillectomy + lingual tonsillectomy)            │
│                                                                            │
│  LIKELY PRIMARY SITES:                                                     │
│  Tonsil (40%) > Tongue base (30%) > Nasopharynx > Hypopharynx/Larynx    │
│                                                                            │
│  MODERN DETECTION RATES:                                                   │
│  PET-CT: 24-37% | Panendoscopy: 17-40% | TORS/TLM: 60-94%               │
│                                                                            │
│  p16+ HPV-related CUP: 68-80% of cases (oropharyngeal origin)           │
│  EBV-related CUP: Nasopharyngeal origin                                   │
│                                                                            │
│  TREATMENT:                                                                │
│  Surgery (ND) + PORT ± Chemotherapy (Cisplatin/Cetuximab)                │
│  RT: Unilateral (p16+, N1-2) vs. Total mucosal (p16-, N3, ENE+)         │
│  IMRT preferred; Immunotherapy emerging                                   │
│                                                                            │
│  PROGNOSIS:                                                                │
│  HPV+: 75-80% 5-year survival | HPV-: 30-40% | Overall: ~50%            │
└────────────────────────────────────────────────────────────────────────────┘

REFERENCES (Standard Textbooks and Articles)

1. Scott-Brown's Otorhinolaryngology Head & Neck Surgery, Chapter 17 - "Carcinoma of Unknown Primary" (Simo, Jeannon, Guerrero Urbano) - 8th Edition
2. Cummings Otolaryngology Head and Neck Surgery, Chapter 96 - "Unknown Primary" (Karni et al. TLM approach, HPV paradigm) - 7th Edition
3. K.J. Lee's Essential Otolaryngology - 11th Edition - Chapter on Neck Mass and Unknown Primary
4. Dhingra's Diseases of Ear, Nose and Throat - Chapter on Cervical Lymphadenopathy and Neck Mass
5. Hazarika's Textbook of Ear, Nose and Throat - Section on Head and Neck Oncology
6. Stell and Maran's Head and Neck Surgery - Chapter on Cervical Metastases and Unknown Primary
7. Zakir Hussain's ENT (for clinical approach and Indian perspective)
8. Al-Lami A et al. "Reducing the unknowns: A systematic review & meta-analysis of transoral surgical techniques in CUP." Oral Oncology 2022. [PMID: 35144209]
9. Kalavacherla S et al. "Updates in the management of unknown primary of the head and neck." Frontiers in Oncology 2022. [PMID: 36185196]
10. Chabrillac E et al. "Narrow-Band Imaging in oncologic otorhinolaryngology: State of the art." Eur Ann Otorhinolaryngol 2021. [PMID: 33722467]
11. Maghami E et al. "Diagnosis and Management of SCC of Unknown Primary in the Head and Neck: ASCO Guideline." J Clin Oncol 2020. [38:2570-96]
12. AJCC Cancer Staging Manual 8th Edition (2017) - Head and Neck TNM

Exam Tip for RGUHS: Always start with the definition from Scott-Brown's (Chapter 17), draw the investigation flow chart with 5 steps (FNL → FNAC → CT → PET-CT → Panendoscopy → TORS), include the cervical node level-to-primary site table, and end with recent advances (NBI, TORS, HPV de-escalation, immunotherapy). The branchiogenic cyst vs. CUP distinction and "no open biopsy" rule always carry marks.