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QUESTION 3 (20 Marks)

Classification of Bone Tumors + Microscopic Variants of Osteogenic Sarcoma

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PART A: CLASSIFICATION OF BONE TUMORS

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I. PRIMARY BONE TUMORS

A. Bone-Forming (Osteogenic) Tumors

B. Cartilage-Forming (Chondrogenic) Tumors

C. Fibrous and Fibrohistiocytic Tumors

D. Giant Cell Tumor (Osteoclastoma)

• Locally aggressive; classified separately
• Most commonly at epiphysis of long bones
• Grade I, II, III (with Grade III being frankly malignant)

E. Marrow (Myelogenic) Tumors

F. Vascular Tumors

G. Other Tumors

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II. SECONDARY (METASTATIC) BONE TUMORS

• Most common bone tumors in adults overall
• Primary sites: Breast, Lung, Prostate, Kidney, Thyroid (mnemonic: BLPKiT or "Bad Luck Puts Kidney in Trouble")
• Prostate: osteoblastic metastases
• Kidney, thyroid: osteolytic metastases
• Breast and lung: mixed

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WHO Classification Summary (by tissue type)

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PART B: MICROSCOPIC VARIANTS OF OSTEOGENIC SARCOMA (OSTEOSARCOMA)

General Histological Features (All Variants)

• Pleomorphic spindle or polygonal tumor cells
• Direct production of osteoid by tumor cells (sine qua non of diagnosis)
• High mitotic activity, atypical mitoses
• Variable amounts of cartilage, fibrous tissue
• Tumor giant cells

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MICROSCOPIC VARIANTS OF OSTEOSARCOMA

1. Conventional (Classic) Osteosarcoma - High Grade, Intramedullary

• Dominant matrix: lace-like or trabecular osteoid/woven bone produced directly by malignant cells
• Cells: pleomorphic spindle/polygonal osteoblast-like cells
• Osteoid appears as pink, amorphous material deposited between tumor cells
• Differentiating feature: osteoid laid down directly by malignant cells (not reactive)

• Dominant matrix: chondroid/cartilaginous
• Hyaline or myxoid cartilage produced by atypical chondrocyte-like cells
• Osteoid still present but in lesser amounts - may be focal
• Must be distinguished from chondrosarcoma (by presence of osteoid)
• Lobular arrangement of chondroid tissue with peripheral enhancement

• Dominant matrix: fibrous/spindle cell pattern (resembles fibrosarcoma or MFH)
• Herringbone or storiform pattern of spindle cells
• Osteoid is minimal and may be sparse/focal
• High grade cytology with pleomorphism; still qualifies as osteosarcoma due to osteoid production

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2. Telangiectatic Osteosarcoma

• Gross: Large blood-filled cavities resembling aneurysmal bone cyst
• Micro: Spaces filled with blood, separated by thin septa
• Septa lined by malignant cells (not endothelial cells)
• Sparse osteoid between the septa
• Cells show marked pleomorphism; atypical giant cells within septa
• Poor prognosis historically; responds well to chemotherapy

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3. Small Cell Osteosarcoma

• Composed of small, round blue cells resembling Ewing's sarcoma
• Must be distinguished from Ewing's: focal osteoid production is key
• Cells are uniform, hyperchromatic, scant cytoplasm
• CD99 can be positive (mimicking Ewing's) - osteoid production or immunophenotype (SATB2+) helps differentiate
• Rare; high grade

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4. Low-Grade Central (Intramedullary) Osteosarcoma

• Well-differentiated; cytologically bland spindle cells
• Produces well-formed bony trabeculae with minimal cytological atypia
• Resembles fibrous dysplasia histologically - diagnosis requires clinical + radiological correlation
• Low mitotic rate; minimal pleomorphism
• Can dedifferentiate to high-grade osteosarcoma

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5. Parosteal (Juxtacortical) Osteosarcoma

• Arises on the outer surface (periosteum/cortex) of bone - posterior distal femur is classic
• Micro: Well-differentiated spindle cells in fibrous stroma with well-formed, parallel bony trabeculae
• Low nuclear grade; bland spindle cells between trabeculae
• Resembles normal cancellous bone but lacks the normal organization
• May contain cartilage cap (like osteochondroma)
• Prognosis: best among all osteosarcomas; rarely metastasizes

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6. Periosteal Osteosarcoma

• Intermediate between parosteal and conventional
• Predominantly chondroblastic with prominent lobular cartilaginous component
• Arises from periosteum; surface lesion of bone
• Tumor cells: chondrocyte-like within lobules; osteoid in periphery of lobules
• Intermediate grade

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7. High-Grade Surface Osteosarcoma

• Rare; arises on surface but is high grade
• Histologically identical to conventional high-grade osteosarcoma
• Poor prognosis

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Summary Table: Osteosarcoma Variants

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QUESTION 4 — SHORT NOTES (10 marks each)

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4(a) Causes of Portal Hypertension

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Classification of Causes

I. Pre-hepatic (Pre-sinusoidal, Extrahepatic)

• Portal vein thrombosis - most common cause of extrahepatic portal hypertension (neonatal omphalitis, hypercoagulable states, abdominal sepsis, tumor compression)
• Splenic vein thrombosis - secondary to pancreatitis, pancreatic tumor; causes isolated gastric varices (sinistral/left-sided portal hypertension)
• Arterio-portal fistula - increased portal blood flow
• Massive splenomegaly (tropical splenomegaly / Banti syndrome) - increased splenic blood flow
• Extrinsic compression of portal vein (lymph nodes, tumor)

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II. Intrahepatic Causes

• Schistosomiasis - most common cause of portal hypertension worldwide; periportal granulomatous fibrosis (pipestem fibrosis of Symmers)
• Congenital hepatic fibrosis
• Primary biliary cirrhosis (early stages)
• Sarcoidosis - portal granulomas
• Drugs and toxins (arsenic, vinyl chloride)
• Myeloproliferative disorders (myeloid metaplasia)
• Non-cirrhotic portal fibrosis (idiopathic portal hypertension)

• Cirrhosis - the most common cause in the Western world
  • Alcoholic cirrhosis (most common)
  • Post-viral cirrhosis (HBV, HCV)
  • Post-necrotic / cryptogenic cirrhosis
  • Biliary cirrhosis
  • Metabolic-associated steatotic liver disease (MASLD)
• Mechanism in cirrhosis: fibrosis + regenerative nodules distort sinusoidal architecture, increase vascular resistance; also increased splanchnic blood flow

• Veno-occlusive disease (sinusoidal obstruction syndrome) - caused by high-dose chemotherapy, bone marrow transplantation, pyrrolizidine alkaloids (bush tea)
• Alcoholic hepatitis with central vein fibrosis

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III. Post-hepatic (Suprahepatic / Post-sinusoidal Extrahepatic)

• Budd-Chiari syndrome - hepatic vein thrombosis (polycythemia vera, hypercoagulable states, pregnancy, OCP use, paroxysmal nocturnal hemoglobinuria); presents with hepatomegaly, ascites, abdominal pain
• Inferior vena cava obstruction (membranous web, thrombosis)
• Constrictive pericarditis
• Right heart failure / Tricuspid regurgitation - back pressure transmitted to hepatic veins

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Consequences of Portal Hypertension

• Esophageal and gastric varices (risk of catastrophic hemorrhage)
• Splenomegaly with hypersplenism (pancytopenia)
• Ascites (with hypoalbuminemia, sodium retention)
• Caput medusae (prominent abdominal wall veins)
• Hepatorenal syndrome
• Hepatic encephalopathy
• Porto-pulmonary hypertension / hepatopulmonary syndrome

Sources: Bailey and Love's Short Practice of Surgery, 28th Ed.; Sleisenger and Fordtran's Gastrointestinal and Liver Disease

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4(b) Molecular Model of Evolution of Colorectal Cancer (Adenoma-Carcinoma Sequence)

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I. Chromosomal Instability (CIN) Pathway - The Classic Vogelstein Model (~70% of CRC)

• APC (adenomatous polyposis coli) is a tumor suppressor gene
• Normally, APC promotes degradation of beta-catenin (Wnt pathway regulation)
• Loss of APC leads to nuclear accumulation of beta-catenin, activating proliferative genes (MYC, cyclin D1)
• This is the initiating event - converts normal epithelium to early adenoma
• Germline APC mutation = Familial Adenomatous Polyposis (FAP)

• Activating point mutation in KRAS oncogene (codons 12/13)
• KRAS encodes a GTPase in the RAS-MAP kinase signaling pathway
• Results in constitutive, growth-factor-independent cell proliferation
• Drives progression from small to large/intermediate adenoma

• Loss of 18q LOH (loss of heterozygosity) occurs in intermediate to advanced adenoma
• SMAD2/4 are effectors of TGF-beta tumor suppressor pathway
• DCC (deleted in colorectal carcinoma) gene loss also occurs here
• Loss leads to evasion of growth inhibitory signals

• TP53 is the "guardian of the genome"
• Loss allows cells with DNA damage to survive and proliferate
• This step drives the transition from advanced adenoma to invasive carcinoma
• Loss of p53 is the most important late event in carcinogenesis

Normal epithelium
    → APC loss (chromosome 5q) → Early adenoma
    → KRAS activation → Intermediate adenoma
    → SMAD4/DCC loss (18q) → Advanced adenoma
    → TP53 loss (17p) → Invasive carcinoma
    → Additional mutations → Metastatic carcinoma

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II. Mismatch Repair (MMR) Deficiency Pathway - Microsatellite Instability (MSI) (~15% of CRC)

• Defective DNA mismatch repair (MMR) results in accumulation of mutations at simple repeat sequences (microsatellite instability - MSI-high)
• Key MMR genes: MLH1, MSH2, MSH6, PMS2
• Sporadic MSI-high CRC: caused by hypermethylation (silencing) of MLH1 promoter
• Lynch syndrome (Hereditary Non-Polyposis CRC, HNPCC): germline mutation in MMR genes (most commonly MLH1 or MSH2)
• Mutations accumulate in genes with microsatellite sequences within coding regions: TGFβRII, BAX, PTEN, MLH3
• MSI-high tumors: right-sided, poor differentiation (mucinous, signet ring), lymphocytic infiltration, better prognosis despite poor histology
• Clinically important: MSI-high tumors respond dramatically to PD-1/PD-L1 immune checkpoint inhibitors (pembrolizumab), but are less sensitive to 5-FU

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III. CpG Island Methylation Phenotype (CIMP) (~15-20% of CRC)

• Widespread promoter hypermethylation silences tumor suppressor genes
• BRAF V600E mutation is frequently associated (instead of KRAS)
• Tumors often right-sided, associated with methylation silencing of MLH1
• Can be MSI-high or microsatellite stable (MSS)
• CIMP/BRAF/MSI-high tumors are associated with the sessile serrated adenoma pathway

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Key Genes Involved

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Hereditary CRC Syndromes - Brief Note

• FAP: germline APC mutation; hundreds of polyps; near 100% CRC risk untreated; autosomal dominant
• Lynch syndrome (HNPCC): germline MLH1/MSH2/MSH6/PMS2 mutation; increased risk of CRC, endometrial, ovarian, urinary cancers; Amsterdam criteria for diagnosis
• MUTYH-associated polyposis: autosomal recessive; base excision repair defect

Source: Harrison's Principles of Internal Medicine, 22nd Ed.; Clinical Gastrointestinal Endoscopy, 3rd Ed.

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4(c) Prostatic Intraepithelial Neoplasia (PIN)

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Definition

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Grading

• Nuclear enlargement but nucleoli inconspicuous or small
• Mild architectural crowding
• Basal cell layer intact
• Not considered clinically significant
• Not reported on biopsy reports as it has no management implications
• Found in men as young as 20-30 years

• Clinically significant; well-established precursor to invasive carcinoma
• Large prominent nucleoli (resembling invasive carcinoma nuclei)
• Irregular nuclear spacing, nuclear crowding
• Partial or focally attenuated (but not absent) basal cell layer
• Intact basement membrane (distinguishes from invasive carcinoma)
• Found in approximately 80% of prostatic tissue removed for carcinoma

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Architectural Patterns of HGPIN

1. Tufting (most common, ~97%) - micropapillary projections without fibrovascular cores
2. Micropapillary - thin papillary projections into lumen without fibrovascular cores
3. Cribriform - bridging of glandular lumen by atypical cells forming sieve-like pattern
4. Flat - single or few cell layers of atypical cells lining acinar walls

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Microscopic Features of HGPIN

• Architecturally benign, large glands/acini
• Luminal cells: enlarged nuclei, prominent nucleoli (similar to carcinoma - key feature)
• Chromatin clearing (vesicular nucleus)
• Cytologically atypical cells identical to carcinoma
• Basal cell layer: present but attenuated/focally absent (demonstrated by p63, HMWCK immunostain)
• Basement membrane: intact (contrast with invasive carcinoma - no BM)
• AMACR (alpha-methylacyl-CoA racemase): may show weak/focal positivity in HGPIN (strong and diffuse in carcinoma)

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Relationship to Prostatic Carcinoma

• HGPIN is found in ~80% of prostatic tissues harboring carcinoma (Robbins Pathology)
• Molecular studies show both HGPIN and adenocarcinoma share identical genetic abnormalities:
  • Loss of NKX3.1 (8p)
  • TMPRSS2-ERG gene fusion
  • Loss of PTEN
  • Telomere shortening
• HGPIN precedes carcinoma by approximately 10 years
• Adjacent to carcinoma in 80% of cases; multifocal in distribution
• Basal cells are progressively lost as HGPIN transitions to invasive carcinoma

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Clinical Significance and Management

• HGPIN on needle biopsy: Risk of detecting carcinoma on repeat biopsy is increased - approximately 20-30% of men will have carcinoma on repeat biopsy within 5 years
• PSA may be mildly elevated
• Isolated HGPIN: Not treated; patient placed on active surveillance with repeat biopsy at 6-24 months
• Biomarker tests (PCA3, 4K score, PHI) may guide rebiopsy decisions
• Extensive HGPIN (3+ cores) warrants earlier and more careful follow-up

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Differential Diagnosis of HGPIN

Source: Robbins, Cotran & Kumar Pathologic Basis of Disease; Campbell-Walsh-Wein Urology

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4(d) Role of FNAC in Diagnosis of Salivary Gland Lesions

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Indications for FNAC in Salivary Gland Lesions

• Any discrete parotid, submandibular, or sublingual swelling
• Differentiation of neoplastic from non-neoplastic lesions
• Differentiation of benign from malignant tumors pre-operatively
• To plan surgical approach and extent of surgery
• Suspected lymph node vs. salivary gland origin
• Post-operative follow-up for tumor recurrence
• Contraindication to surgery (staging/palliation planning)

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Technique

• 21-23 gauge needle, 10 mL syringe; aspiration under negative pressure
• Ultrasound-guided FNAC improves accuracy and "hit rate" significantly
• Multiple passes from different angles improve cellularity
• Air-dried smears (Giemsa/Diff-Quik) and alcohol-fixed smears (Papanicolaou/H&E)
• Special stains (PAS, mucicarmine) and cell blocks can be prepared

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Cytological Diagnosis of Common Salivary Gland Lesions

• Cellular smear: epithelial cells + myoepithelial cells + fibrillary/myxoid stroma
• Epithelial cells: ductal cells in sheets/tubules
• Myoepithelial cells: plasmacytoid or spindle shaped (key feature)
• Characteristic metachromatic fibrillary chondromyxoid stroma (magenta on Giemsa)
• FNAC sensitivity: high; but may be non-diagnostic if tumor is heavily fibrous

• Oncocytic cells (granular, eosinophilic cytoplasm) in papillary clusters
• Background: lymphocytes (characteristic) and debris (foamy macrophages)
• Cystic fluid often brown/murky
• Virtually pathognomonic cytological picture

• Low grade: mucous cells, epidermoid cells, intermediate cells; few mucin pools
• High grade: predominantly epidermoid cells, few mucous cells; marked atypia
• Mucin pools in background (PAS-positive)
• Difficult to grade on FNAC alone

• Characteristic cylindromatous appearance: globoid hyaline cylinders/spheres of basement membrane material
• Basaloid cells arranged around the cylinders in a cribriform or trabecular pattern
• Cells: small, hyperchromatic, uniform; scant cytoplasm
• Highly specific cytological appearance; facilitates pre-operative planning for nerve-sparing

• Large cells with abundant granular cytoplasm (serous/zymogen granules - PAS+)
• Clear or vacuolated cytoplasm; round eccentric nuclei
• Low N:C ratio; relatively low-grade appearance
• Loose acinar clusters; single cells in background

• Markedly atypical large epithelial cells
• Comedonecrosis in background; similar to breast ductal carcinoma (HER2 overexpression)
• Pleomorphic, irregular nuclei, prominent nucleoli

• Sialadenitis (acute/chronic): neutrophils/lymphocytes, ductal cells, no significant atypia
• Sjogren's syndrome: lymphocytes, acini, ductal cells; ductal squamous metaplasia
• Sialadenosis: enlarged acinar cells, abundant zymogen granules; no inflammation
• Lymphoepithelial lesion: lymphoid tissue with epithelial islands

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Accuracy and Limitations

• Inadequate/non-diagnostic samples (especially in fibrotic/sclerotic lesions)
• Cannot always distinguish between different malignant subtypes
• Cannot assess capsular invasion (needed to diagnose malignancy in some entities)
• False negative rate of ~5-10% (sampling error)
• Cystic lesions may yield only fluid with few cells

• Less invasive, simple office procedure
• No risk of facial nerve injury
• Rapid result; can be done at point-of-care (one-stop clinic with ultrasound)
• No seeding risk (controversial but generally not an issue with either technique)

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Role in Management Algorithm

Salivary gland swelling
    ↓
Ultrasound ± FNAC (one-stop clinic)
    ↓
FNAC result:
    Benign (e.g., pleomorphic adenoma) → Plan elective superficial parotidectomy
    Malignant → Staging workup (CT/MRI, chest imaging) → Radical surgery ± radiotherapy
    Suspicious / Atypical → Core needle biopsy or repeat FNAC
    Non-diagnostic → Repeat FNAC under ultrasound guidance

• Non-diagnostic FNAC on repeat
• FNAC suggests possible malignancy (needs tissue architecture for subtyping)
• Some centers use core biopsy primarily (sensitivity 100%, specificity 92% in selected series)

Sources: Scott-Brown's Otorhinolaryngology Head & Neck Surgery; Cummings Otolaryngology Head and Neck Surgery, 7th Ed.

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