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PA6.1-7 | Neoplasia — PBL Case

CLINICAL SETTING

Divya, a 22-year-old postgraduate student from Chennai, presents to the gynaecology OPD at a tertiary care hospital with a 3-month history of lower abdominal fullness and an episode of acute torsion-like pain that resolved spontaneously. An ultrasound performed at a private clinic shows a 9 cm right ovarian mass with mixed echogenicity — areas of cystic, solid, and calcified components, with 'acoustic shadowing' from a tooth-like density. Serum AFP is 320 IU/mL (normal <10), serum β-hCG is undetectable, and CA-125 is mildly elevated at 62 U/mL (normal <35). A CT scan confirms the ovarian mass and shows a 1.2 cm enlarged right external iliac lymph node. She is referred to a specialist centre. On examination, the mass is palpable in the right iliac fossa, non-tender, firm, and partially mobile. The gynaecological oncologist says: 'This is a complex ovarian mass in a young woman — before we operate, we need to understand what kind of tumour this could be and why it matters enormously to get it right.' Divya and her family ask: Is it cancer?

Trigger 1: What Kind of Tumour Is This?

The multidisciplinary team reviews the imaging. The radiologist describes the mass as having: (a) a thick-walled cystic component with internal echoes; (b) a solid nodular component (Rokitansky protuberance) containing a calcification resembling a tooth; (c) areas of fat density on CT (Hounsfield −80 to −120). Based on this imaging appearance, the lead pathologist provisionally considers two possibilities: a mature cystic teratoma (dermoid cyst) and an immature teratoma or mixed germ-cell tumour. She explains that both arise from germ cells, but their biological behaviour — and therefore their clinical management — is radically different. She adds: 'The elevated AFP in a young woman with an ovarian mass should never be dismissed.'

DISCUSSION POINTS

  • Define neoplasia and classify it using the two-component framework (parenchyma and stroma). Using the nomenclature rules, explain what a 'teratoma' is — which germ layers are represented, and why teratomas are classified differently from carcinomas and sarcomas?
  • Both a mature cystic teratoma and an immature teratoma arise from the same cell of origin (germ cells), yet they have radically different clinical behaviours. Using the five characteristics that distinguish benign from malignant neoplasms — differentiation/anaplasia, rate of growth, local invasion, metastasis, and capsule — compare the two.
  • The AFP is 320 IU/mL. AFP is a tumour marker. Explain what tumour markers are, why they are NOT diagnostic on their own, and which specific germ-cell tumour components produce AFP vs β-hCG vs LDH. Why is Divya's undetectable β-hCG reassuring against one specific germ-cell tumour type?
  • The enlarged right external iliac lymph node on CT may represent metastasis. Describe the routes by which ovarian neoplasms metastasize: lymphatic (which node chains), haematogenous (which organs), and transcoelonic (which surfaces in the peritoneal cavity). Explain Paget's 'seed and soil' hypothesis and which 'soils' are most permissive for ovarian cancer.
Click to reveal Trigger 2: Inside the Specimen (discuss previous trigger first!)

Trigger 2: Inside the Specimen

Divya undergoes right salpingo-oophorectomy with lymph node sampling. Gross specimen (38 cm³ ovary): capsule intact, outer surface smooth. Cut surface: multiloculated cystic cavity containing hair, sebaceous material, and a solid protuberance with a rudimentary tooth; no haemorrhage or necrosis. The adjacent 1.2 cm lymph node shows a firm white nodule. Histopathology report: 'Primary specimen — Mature cystic teratoma (dermoid cyst) with foci of immature neuroepithelium (Grade 2 immature teratoma, WHO). Lymph node — 1/1 positive for metastatic germ-cell tumour; no lymphovascular invasion identified in primary. Mitotic count: 12/10 HPF. Margins: free.' The pathologist emphasises: 'The mature dermoid cyst component fooled the pre-operative imaging — but the immature neuroepithelium and the lymph node metastasis confirm this is a malignant germ-cell tumour.' The oncologist now needs to counsel Divya about systemic therapy.

DISCUSSION POINTS

  • The gross specimen shows an intact smooth capsule with hair, sebaceous material, and a tooth — classic features of a mature cystic teratoma (dermoid). The histopathology, however, finds foci of immature neuroepithelium. Explain the significance of this microscopic finding: why does immaturity of the neuroepithelial component change the diagnosis from benign to malignant?
  • The pathologist grades the tumour as Grade 2 (WHO). Explain the concepts of histological grading and tumour staging, and contrast them: what does each communicate about the tumour, and which has the greater immediate impact on Divya's prognosis and treatment planning?
  • Mitotic count is 12/10 HPF. Explain how an abnormally high mitotic count reflects dysregulation of the cell cycle in cancer — name the specific cell cycle checkpoints (G1/S checkpoint involving p53/Rb, M checkpoint involving spindle assembly), the oncogenes that drive unchecked replication (MYC, cyclin D1-CDK4), and the tumour suppressor genes whose loss removes the brakes.
  • The lymph node shows metastatic germ-cell tumour. Describe the sequential steps of metastasis — local invasion (basement membrane degradation by MMPs), intravasation, survival in circulation, extravasation, and colonisation. Which of these steps is rate-limiting, and what molecule is most critical for the invasion step?
Click to reveal Trigger 3: The Bigger Picture — Why Did This Happen and What Comes Next? (discuss previous trigger first!)

Trigger 3: The Bigger Picture — Why Did This Happen and What Comes Next?

Divya's oncologist discusses adjuvant chemotherapy (BEP regimen — bleomycin, etoposide, cisplatin). During the counselling session, Divya's mother asks: 'Why did a perfectly healthy 22-year-old develop cancer? We eat well, we don't smoke.' The oncologist explains that germ-cell tumours are largely sporadic, driven by epigenetic and chromosomal instability during meiosis in young women, not by environmental carcinogens. He adds: 'But your mother's question is exactly the right question in cancer biology.' Post-chemotherapy, Divya's AFP normalises to 6 IU/mL. At a follow-up three months later, a new complaint emerges: she has difficulty breathing, fatigue, and chest X-ray shows bilateral patchy infiltrates. The oncologist suspects bleomycin pulmonary toxicity — a non-metastatic, non-paraneoplastic complication. However, a paraneoplastic syndrome is also on the differential: the residual tumour could be producing an anti-neural antibody causing inflammatory lung injury. Her PET-CT shows no residual tumour.

DISCUSSION POINTS

  • Divya's mother asks why a healthy young woman develops cancer. Explain multistep carcinogenesis using the concept of sequential mutation acquisition — even in a young patient without environmental carcinogens, spontaneous mutations during rapid germ-cell proliferation and epigenetic dysregulation can initiate malignant transformation. Name the categories of carcinogens (chemical, radiation, microbial) and explain why germ-cell tumours differ in their carcinogenic mechanisms from, say, cervical carcinoma (HPV-driven) or HCC (aflatoxin + HBV).
  • Explain tumour immunology in Divya's context: (a) what immune surveillance mechanisms should have detected her tumour early? (b) which immune evasion mechanisms allowed the tumour to grow to 9 cm before clinical detection? (c) how does immune checkpoint blockade (anti-PD-1/PD-L1 therapy) attempt to reverse tumour-driven immune suppression?
  • A paraneoplastic syndrome is suspected. Define paraneoplastic syndrome and give TWO examples relevant to germ-cell and gynaecological tumours (e.g., anti-NMDAR encephalitis in ovarian teratoma, hypercalcaemia in ovarian clear-cell carcinoma). Explain why paraneoplastic syndromes can precede, coincide with, or follow tumour diagnosis, and why treating the tumour may resolve the syndrome.
  • Divya's AFP normalised after chemotherapy. How is tumour marker kinetics (half-life, rate of decline, nadir) used to monitor treatment response and detect relapse? Compare AFP, CA-125, and CEA in terms of their sensitivity, specificity, and appropriate clinical use — and why no tumour marker should be used as a screening test in the general population.

Group Task Assignments

Group 1: Neoplasm nomenclature, classification, and the benign vs malignant spectrum

  • Build a classification tree of ovarian neoplasms: (a) surface epithelial tumours (serous, mucinous, endometrioid — benign vs borderline vs malignant); (b) germ-cell tumours (mature teratoma, immature teratoma, dysgerminoma, yolk sac tumour, choriocarcinoma); (c) sex-cord stromal tumours (granulosa cell, Sertoli-Leydig). For each category, list the tumour marker(s) and the dominant age group.
  • Using Divya's gross specimen, prepare a mock gross description using the systematic 4-step protocol: organ identification, size/weight, margin character, and cut-surface appearance. Predict the histological pattern from the gross description alone.

Competencies: PA6.1, PA6.7

Group 2: Molecular basis of cancer — oncogenes, TSGs, and the cell cycle

  • Map the molecular events in carcinogenesis on a cell-cycle diagram: show where cyclin D1-CDK4 complex drives G1/S progression, where Rb normally functions as a brake, and how loss of p53 allows bypassing the G1/S checkpoint. Add MYC (growth signal) and BCL2 (apoptosis suppression) at their correct positions.
  • Research and present: How does p53 normally respond to DNA damage — describe the sequence from DNA break → ATM/ATR activation → p53 stabilisation → p21 induction → cell cycle arrest → either repair or apoptosis. Why is p53 mutated in >50% of all human cancers?

Competencies: PA6.2

Group 3: Carcinogenesis — chemical, radiation, and microbial

  • Compare three types of carcinogens using a structured table: chemical (direct-acting vs procarcinogen requiring metabolic activation), radiation (UV vs ionising — mechanism and target cancer), and microbial (HPV vs HBV/HCV vs H. pylori — mechanism and associated cancer). Include one Indian public-health example for each.
  • Explain why Divya's germ-cell tumour is NOT primarily driven by exogenous carcinogens, using the concept of genomic instability during meiosis, isochromosome 12p (characteristic of germ-cell tumours), and epigenetic silencing of tumour suppressor genes in gonadal cells.

Competencies: PA6.3

Group 4: Tumour effects on the host and paraneoplastic syndromes

  • Classify Divya's systemic manifestations: (a) weight loss and fatigue — is this cancer cachexia? Describe the cytokine-driven mechanism (TNF-α, IL-1, IL-6) and why it differs from simple starvation; (b) elevated AFP — local effect vs systemic marker; (c) proposed anti-neural antibody-mediated lung injury — paraneoplastic vs treatment toxicity. For each, state whether it is a direct tumour effect, paraneoplastic effect, or treatment complication.
  • Prepare five paraneoplastic syndrome flash cards: each showing tumour type, mediator/mechanism, clinical syndrome, and laboratory finding. Include: SIADH (SCLC/ADH), ectopic ACTH (SCLC/CRH-ACTH), hypercalcaemia of malignancy (PTHrP), anti-NMDAR encephalitis (ovarian teratoma/anti-NMDAR antibody), Trousseau syndrome (pancreatic/mucin-mediated platelet activation).

Competencies: PA6.4, PA6.7

Group 5: Tumour immunology, laboratory diagnosis, and tumour markers

  • Explain the immune landscape of ovarian germ-cell tumours: (a) which tumour-associated antigens (TAAs) could the immune system recognise? (b) how does PD-L1 expression on tumour cells suppress T-cell attack? (c) why does immune checkpoint blockade (pembrolizumab/nivolumab) restore anti-tumour immunity? Relate this to Divya's post-chemotherapy surveillance.
  • Design a tumour marker monitoring protocol for Divya over 2 years post-chemotherapy: specify which markers to measure (AFP, β-hCG, LDH), at what intervals, what constitutes a 'rising marker' threshold for concern, and which imaging modality complements marker surveillance. Discuss the principles of sensitivity vs specificity for tumour markers in follow-up vs screening contexts.

Competencies: PA6.5, PA6.6

Learning Issues

Research these questions and bring your findings to the discussion.

  1. [PA6.1] What is the definition of neoplasia (Willis)? How is a teratoma classified and named — what makes it a special category distinct from carcinoma and sarcoma? How do the five characteristics of benign vs malignant neoplasms apply to the contrast between a mature cystic teratoma and an immature teratoma?
  2. [PA6.2] What are the molecular mechanisms that drive cancer — how do proto-oncogenes become oncogenes, and what do tumour suppressor genes normally do? Describe the role of p53 in the DNA damage response and why its loss is so commonly selected for in malignant transformation.
  3. [PA6.3] What are the three categories of carcinogens — chemical, radiation, and microbial — and what is the mechanism by which each causes DNA damage? Why does Divya's germ-cell tumour differ from HPV-driven cervical cancer or aflatoxin-driven hepatocellular carcinoma in its carcinogenic mechanism?
  4. [PA6.4] What are the local and systemic effects of cancer on the host? What is cancer cachexia and what cytokines drive it? Describe the paraneoplastic syndromes most relevant to germ-cell and ovarian tumours.
  5. [PA6.5] What is a tumour marker, and what are its limitations as a diagnostic tool? For AFP, β-hCG, CA-125, and CEA, describe the associated tumour, normal serum level, clinical use, and key limitation. How is tumour marker kinetics used to monitor treatment response?
  6. [PA6.6] What is immune surveillance, and what evidence supports it? How do tumours evade immune recognition — describe antigen loss, MHC downregulation, PD-L1 upregulation, and Treg recruitment. How does immune checkpoint blockade reverse PD-L1-mediated immune suppression?
  7. [PA6.7] What are the histological features that distinguish benign from malignant neoplasms on a biopsy slide? How does tumour grading differ from staging, and what does each communicate about prognosis?