Make notes of respiratory system according to md pathology using robins and ackerman book. Including sll important questions that can come from this chapter for md pathology exam
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Molecular and prognostic marker of lung carcinoma
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lung carcinoma molecular markers prognostic
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Now I have everything I need. Here are comprehensive notes on molecular and prognostic markers of lung carcinoma, drawn from Robbins Basic Pathology and Murray & Nadel's Respiratory Medicine.
Molecular & Prognostic Markers of Lung Carcinoma
(Robbins Basic Pathology + Murray & Nadel's Respiratory Medicine)
1. OVERVIEW — WHY MOLECULAR MARKERS MATTER
- ~50% of non-squamous NSCLC harbour a known, targetable driver mutation
- Driver mutations confer evolutionary growth/survival advantages and are clonally preserved — they define the tumor's behaviour and treatment response
- Next-generation sequencing (NGS) of every locally advanced or metastatic adenocarcinoma is now the standard of care
- Panel-based NGS is superior to single-gene testing — detects mutations, fusions, copy number alterations and RNA rearrangements in one test
- Liquid biopsy (circulating tumour DNA from blood) is used at diagnosis AND at progression to detect resistance mutations
Mutation frequency varies significantly by geographic origin, environmental exposure, and tobacco use. — Murray & Nadel's Respiratory Medicine
2. DRIVER MUTATIONS — MOLECULAR TARGETS
Proportion of NSCLC Driver Mutations (AACR GENIE data):
A. EGFR / HER2 (ERBB1/ERBB2) PATHWAY
| Feature | Details |
|---|---|
| Gene | EGFR (ERBB1) — receptor tyrosine kinase |
| Mechanism | Constitutive activation → ERK, Akt, c-SRC → cyclin D1 → uncontrolled proliferation |
| Common mutations | Exon 19 deletions (most common), L858R point mutation on exon 21 |
| Resistance mutation | T790M on exon 20 — most common cause of acquired resistance to 1st/2nd-gen TKIs |
| Frequency | 9–46% of NSCLC (highest in East Asian females, never-smokers, adenocarcinoma) |
| HER2 (ERBB2) | Mutated in ~3% NSCLC; amplification also seen in subset of adenocarcinomas |
| Targeted drugs | Osimertinib (3rd gen), Erlotinib, Gefitinib, Afatinib, Dacomitinib |
| Prognostic value | Good prognosis with targeted therapy; dramatic improvement in OS vs. EGFR-negative |
Exam point: EGFR mutations are most common in never-smoking Asian women with adenocarcinoma. Exon 19 deletion has slightly better prognosis than L858R.
B. KRAS PATHWAY
| Feature | Details |
|---|---|
| Gene | KRAS — RAS family GTPase (downstream of EGFR) |
| Frequency | ~25–30% of NSCLC (most common in smokers, Western populations) |
| Mutation type | Point mutations (G12C most actionable) |
| Prognosis | Historically poor prognosis; resistance to EGFR-TKIs |
| Targeted drug | Sotorasib (AMG 510) — first approved KRAS G12C inhibitor |
| Key fact | KRAS and EGFR mutations are mutually exclusive |
Exam point: KRAS is the most common oncogene mutated in smoking-related lung adenocarcinoma.
C. ALK / ROS1 / NTRK GENE FUSIONS
| Feature | ALK | ROS1 | NTRK |
|---|---|---|---|
| Mechanism | EML4-ALK fusion → constitutive kinase activity | ROS1 fusion (CD74-ROS1 most common) | NTRK1/2/3 fusions |
| Frequency | ~5% NSCLC | ~1–2% NSCLC | <1% NSCLC |
| Population | Young, never/light smokers, adenocarcinoma | Young, never smokers | Any histology |
| Detection | FISH, IHC, NGS | FISH, NGS | NGS, FISH |
| CNS mets | High propensity — CNS is common "sanctuary" site | Less common | Variable |
| Drugs | Alectinib (1st line), Brigatinib, Ceritinib, Lorlatinib (2nd line) | Crizotinib, Entrectinib | Larotrectinib, Entrectinib |
| Prognosis | Excellent with targeted therapy; resistance inevitable |
Exam point: ALK+ lung cancer — young, non-smoker, adenocarcinoma, signet-ring cell histology. Best response to alectinib (superior to crizotinib in 1st line).
D. BRAF MUTATIONS
| Feature | Details |
|---|---|
| Frequency | ~2–4% NSCLC |
| Key mutation | V600E (most common, ~50% of BRAF-mutated NSCLC) |
| Drugs | Dabrafenib + Trametinib (BRAF + MEK inhibitor combination) |
| Prognosis | Moderate improvement with combination targeted therapy |
E. RET FUSIONS
| Feature | Details |
|---|---|
| Frequency | ~1–2% NSCLC |
| Population | Young, never-smokers, adenocarcinoma |
| Drugs | Selpercatinib, Pralsetinib (highly selective RET inhibitors) |
F. MET (Mesenchymal-Epithelial Transition) Pathway
- MET exon 14 skipping mutations: ~3–4% NSCLC
- Drugs: Capmatinib, Tepotinib
- Also: MET amplification — common acquired resistance mechanism after EGFR-TKI therapy
3. IMMUNOTHERAPY BIOMARKERS
PD-L1 (Programmed Death-Ligand 1)
| Feature | Details |
|---|---|
| Test | IHC — Tumor Proportion Score (TPS) |
| Cutoffs | TPS ≥50% → pembrolizumab monotherapy 1st line; TPS 1–49% → combination chemo-immunotherapy |
| Relevance | Predictive (not purely prognostic) marker for checkpoint inhibitor response |
| Key caveat | PD-L1 expression is lower in oncogene-driven (EGFR/ALK) tumors → immunotherapy less effective in these patients |
TMB (Tumor Mutational Burden)
- High TMB (≥10 mutations/megabase) correlates with better response to checkpoint inhibitors
- Measured by NGS
- Independent of PD-L1 expression
Exam point: In EGFR/ALK+ adenocarcinoma, targeted therapy is always preferred over immunotherapy as 1st line.
4. TUMOR SUPPRESSOR GENES (Robbins Pathology)
| Gene | Role | Lung Cancer Relevance |
|---|---|---|
| TP53 | Cell cycle arrest, apoptosis | Mutated in >50% of all lung cancers (NSCLC + SCLC); especially squamous cell carcinoma |
| RB1 (Retinoblastoma) | G1/S checkpoint | Lost in virtually all SCLC; also lost in some NSCLC |
| CDKN2A (p16/INK4a) | Inhibits CDK4/6 → maintains RB | Deleted/inactivated in adenocarcinoma and squamous |
| STK11 (LKB1) | Serine-threonine kinase | Mutated in ~20% lung adenocarcinoma; associated with KRAS co-mutation and immunotherapy resistance |
| KEAP1/NRF2 | Oxidative stress pathway | Mutated in squamous cell carcinoma; poor prognosis |
| SMARCA4 (BRG1) | SWI/SNF chromatin remodelling | Mutated in ~10% NSCLC; aggressive behaviour |
5. MOLECULAR MARKERS BY HISTOLOGICAL SUBTYPE
Adenocarcinoma (most amenable to targeted therapy)
- EGFR, KRAS, ALK, ROS1, RET, NTRK, BRAF, MET exon 14, HER2
- Immunohistochemistry: TTF-1+, Napsin A+
- Always test for all driver mutations before starting treatment
Squamous Cell Carcinoma
- FGFR1 amplification (~20%) — investigational targets
- EGFR mutations rare (~3%)
- PIK3CA mutations (~10%)
- PDGFRA amplification
- IHC: p40+, p63+, CK5/6+, TTF-1 negative
- PD-L1 expression often higher
Small Cell Lung Cancer (SCLC)
- No known targetable driver mutations currently
- Universal RB1 loss (virtually 100%) + TP53 mutation
- MYCL1/MYCN amplification — drives proliferation
- Neuroendocrine markers: chromogranin A, synaptophysin, CD56, NSE (diagnostic, not targeted)
- DLL3 overexpression — Rovalpituzumab tesirine (investigational)
- Response to platinum-based chemotherapy initially excellent, but almost universal resistance/recurrence
- Immunotherapy (atezolizumab + chemo) now standard in extensive SCLC
Large Cell Neuroendocrine Carcinoma (LCNEC)
- Shares molecular features with SCLC (RB1/TP53) or NSCLC
- Neuroendocrine IHC positive
6. PROGNOSTIC MARKERS — OVERALL
Clinical Prognostic Factors (Robbins)
| Factor | Better Prognosis | Worse Prognosis |
|---|---|---|
| Stage | I, II | III, IV |
| Cell type | Adenocarcinoma (esp. with driver) | SCLC, large cell |
| Resectability | Resectable | Unresectable |
| Performance status | ECOG 0–1 | ECOG 3–4 |
| Weight loss | Absent | >10% body weight |
| Lymph node involvement | N0 | N2/N3 (mediastinal) |
Molecular Prognostic Markers
| Marker | Prognostic Significance |
|---|---|
| EGFR mutation | Good — excellent response to TKIs; better OS than EGFR-wt |
| ALK fusion | Good — excellent response; better OS with alectinib |
| KRAS mutation | Poor historically; improving with KRAS G12C inhibitors |
| TP53 mutation | Poor — especially in NSCLC |
| STK11/LKB1 mutation | Poor — immunotherapy resistance, rapid progression |
| SMARCA4 loss | Poor — aggressive, rapid progression |
| High TMB | Better immunotherapy response (predictive) |
| PD-L1 TPS ≥50% | Better immunotherapy response (predictive) |
| RB1 loss | Very poor — universal in SCLC |
| MYC amplification | Poor — rapid proliferation, chemotherapy resistance |
7. CONCEPTS IN MOLECULAR BIOLOGY OF LUNG CANCER (Robbins/Murray & Nadel)
Hallmarks of Cancer (Hanahan & Weinberg) applicable to lung:
Established (2000): Sustained proliferation, evasion of tumor suppressors, invasion/metastasis, replicative immortality, angiogenesis, resisting apoptosis
Added (2011): Metabolic reprogramming, genomic instability, tumor-promoting inflammation, immune evasion
Carcinogenesis Pathway
- Tobacco carcinogens (PAHs) → Phase I enzymes (CYP1A1) → active carcinogens → DNA adducts → mutations in TP53, KRAS, etc.
- Epigenetic changes → gene silencing (methylation of CDKN2A)
- Chromosomal instability → loss of heterozygosity at 3p, 9p, 17p
- Field cancerization — widespread epithelial DNA damage from carcinogen exposure → multiple independent tumours possible
Epithelial-Mesenchymal Transition (EMT)
- Key step in invasion and metastasis
- Tobacco smoke itself can induce EMT early in carcinogenesis
- Reverse (MET — Mesenchymal-Epithelial Transition) allows establishment at metastatic niche
Tumour Heterogeneity
- Major driver of treatment resistance
- Subclonal populations shift with therapy pressure → clonal selection of resistant clones
- Requires liquid biopsy at progression to detect new resistance mutations
8. RESISTANCE MECHANISMS
| Primary Mutation | Common Resistance Mechanism |
|---|---|
| EGFR exon 19 del / L858R (1st/2nd-gen TKI) | T790M exon 20 mutation → use Osimertinib |
| EGFR + Osimertinib | C797S mutation, MET amplification, HER2 amplification, histological transformation to SCLC |
| ALK (Crizotinib) | Secondary ALK domain mutations (L1196M, G1202R) → use Alectinib/Lorlatinib |
| KRAS G12C (Sotorasib) | KRAS amplification, Y96D mutation, bypass pathway activation |
9. KEY EXAM QUESTIONS — MD PATHOLOGY
Q1. Which molecular mutation is most common in never-smoking Asian women with lung adenocarcinoma?
A: EGFR mutation (exon 19 deletion or L858R — exon 21)
Q2. What is the most common acquired resistance mutation after EGFR-TKI therapy?
A: T790M mutation (exon 20) — overcome by Osimertinib
Q3. ALK gene rearrangement in lung cancer: typical patient profile?
A: Young, non-smoker/light smoker, adenocarcinoma with signet-ring cell features; EML4-ALK fusion; predilection for CNS metastasis; treated with Alectinib (1st line)
Q4. Name the molecular markers tested routinely in metastatic NSCLC adenocarcinoma.
A: EGFR, KRAS, ALK, ROS1, BRAF V600E, RET, NTRK, MET exon 14, HER2, PD-L1, TMB (by NGS panel)
Q5. Which tumor suppressor gene is lost in virtually ALL small cell lung cancers?
A: RB1 (retinoblastoma gene) — nearly universal loss, along with TP53
Q6. What is the difference between a driver mutation and a passenger mutation?
A: Driver mutations confer selective growth/survival advantage and are clonally preserved; passenger mutations are genetically irrelevant to tumor progression
Q7. Which mutation is associated with immunotherapy resistance despite high tumor mutational burden?
A: STK11/LKB1 mutation (associated with KRAS co-mutation, cold immune microenvironment)
Q8. PD-L1 testing: what cutoff is used for pembrolizumab monotherapy?
A: TPS ≥50% (first line monotherapy); TPS 1–49% → combination chemo-immunotherapy
Q9. KRAS mutation: frequency, typical patient, and first approved targeted drug?
A: ~25–30% NSCLC; smokers, Western populations; KRAS G12C targeted by Sotorasib (AMG 510)
Q10. What is "field cancerization" in the context of lung cancer?
A: Widespread DNA damage from carcinogen (tobacco) exposure across respiratory epithelium, predisposing to multiple independent primary tumors; explains why lung cancer patients can develop second primaries
Q11. Name neuroendocrine markers used in diagnosing SCLC.
A: Chromogranin A, Synaptophysin, CD56, Neuron-Specific Enolase (NSE); also TTF-1+ in ~90% SCLC
Q12. What is liquid biopsy and when is it used in lung cancer management?
A: Blood-based detection of circulating tumour DNA (ctDNA) by sequencing; used at initial diagnosis (if tissue unavailable), at progression (to detect resistance mutations), and for monitoring disease response
Q13. Immunohistochemical profile of adenocarcinoma vs. squamous cell carcinoma?
A: Adenocarcinoma: TTF-1+, Napsin A+; Squamous: p40+, p63+, CK5/6+, TTF-1−
Q14. What molecular subtypes of SCLC are recognized, and what drives their heterogeneity?
A: Defined by transcription factor expression (ASCL1-high, NEUROD1-high, POU2F3-high, YAP1-high); cellular plasticity and subpopulation communication drives chemo-resistance; no targetable driver mutations yet identified
10. SUMMARY TABLE — MOLECULAR MARKERS AT A GLANCE
| Marker | Histotype | Frequency | Drug | Prognosis |
|---|---|---|---|---|
| EGFR exon 19 del / L858R | Adeno | 9–46% | Osimertinib | Good |
| KRAS G12C | Adeno | ~25–30% | Sotorasib | Poor → improving |
| ALK fusion (EML4-ALK) | Adeno | ~5% | Alectinib | Good |
| ROS1 fusion | Adeno | 1–2% | Crizotinib, Entrectinib | Good |
| BRAF V600E | Adeno | 2–4% | Dabrafenib+Trametinib | Moderate |
| RET fusion | Adeno | 1–2% | Selpercatinib | Good |
| NTRK fusion | Any | <1% | Larotrectinib | Good |
| MET exon 14 skip | Adeno | 3–4% | Capmatinib | Moderate |
| HER2 (ERBB2) mutation | Adeno | ~3% | T-DM1 | Moderate |
| TP53 mutation | All | >50% | None targeted | Poor |
| RB1 loss | SCLC | ~100% | None targeted | Very poor |
| PD-L1 TPS ≥50% | Any | Variable | Pembrolizumab | Better immuno Rx |
| High TMB | Any | Variable | Checkpoint inhibitors | Better immuno Rx |
Sources: Murray & Nadel's Textbook of Respiratory Medicine, Chapter 73; Robbins Basic Pathology (Robbins & Kumar); Henry's Clinical Diagnosis & Management by Laboratory Methods
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