Skin, soft tissue and paediatric tumours

6 NEET-PG practice questions on Skin, soft tissue and paediatric tumours, part of Pathology. The first 6 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Easy

   A 61-year-old man has a 1.5 cm irregular, variegated pigmented lesion on his back excised at a district hospital. Histology confirms a superficial spreading melanoma without ulceration, and no lymph nodes are palpable. Which single histological measurement best predicts his prognosis?

   1. AClark level of invasion
   2. BBreslow thickness
   3. CDensity of tumour lymphocytes
   4. DLesion diameter

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   Answer: B · Breslow thickness

   Breslow thickness, measured in millimetres from the granular layer of the epidermis to the deepest invasive tumour cell, is the most important prognostic factor in localised melanoma. It sets the T stage, the width of the re-excision margin and whether sentinel lymph node biopsy is offered. Ulceration also worsens the prognosis. Clark level is no longer used in current staging.

   • A: Clark level describes anatomical depth and has been dropped from current staging.
   • C: Tumour-infiltrating lymphocytes have a minor prognostic role compared with thickness.
   • D: Diameter is used to raise suspicion clinically but does not predict outcome after excision.

2. Question 2 · Easy

   A 2-year-old girl is brought to the gynaecology OPD in Varanasi with blood-stained discharge and a soft, polypoid mass like a bunch of grapes protruding from the vagina. Biopsy shows small round to spindle tumour cells crowded beneath the surface epithelium as a dense 'cambium layer', staining for desmin and myogenin. The diagnosis is:

   1. AYolk sac tumour of the vagina
   2. BEmbryonal rhabdomyosarcoma
   3. CClear cell adenocarcinoma
   4. DFibroepithelial polyp

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   Answer: B · Embryonal rhabdomyosarcoma

   A grape-like polypoid mass in the vagina or bladder of a young child, with a subepithelial cambium layer of desmin- and myogenin-positive cells, is the botryoid form of embryonal rhabdomyosarcoma (sarcoma botryoides). Embryonal rhabdomyosarcoma is the commonest soft tissue sarcoma of children, and the botryoid form has a relatively good prognosis with chemotherapy and conservative surgery.

   • A: Vaginal yolk sac tumour raises AFP and shows Schiller-Duval bodies, not skeletal muscle markers.
   • C: Clear cell adenocarcinoma affects young women, classically after in-utero DES exposure.
   • D: Fibroepithelial polyps lack a cambium layer of myogenin-positive cells.

3. Question 3 · Medium

   A 34-year-old man has a slowly growing, firm, reddish-brown plaque with protruding nodules on the skin of his upper back; it has recurred twice after simple excision at a local clinic. Biopsy shows uniform spindle cells in a storiform (cartwheel) pattern infiltrating deep into the subcutaneous fat in a honeycomb pattern, and the cells are strongly CD34-positive. If the tumour becomes unresectable, which drug targets its molecular driver?

   1. AVemurafenib
   2. BTrastuzumab
   3. CImatinib
   4. DCrizotinib

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   Answer: C · Imatinib

   A storiform spindle-cell tumour that honeycombs into the subcutaneous fat and is strongly CD34-positive is dermatofibrosarcoma protuberans. Most carry a COL1A1::PDGFB fusion, usually from t(17;22), which drives overproduction of PDGF-B and constant activation of the PDGF receptor. Imatinib inhibits this receptor tyrosine kinase and is used for unresectable or metastatic disease. The tumour sends finger-like extensions far beyond the visible edge, so it recurs after simple excision and needs wide or Mohs excision.

   • A: Vemurafenib inhibits mutant BRAF V600E, used in melanoma.
   • B: Trastuzumab targets HER2 in breast and gastric cancer.
   • D: Crizotinib inhibits ALK and ROS1 fusions in lung cancer.

4. Question 4 · Medium

   A 48-year-old woman had a melanoma excised from her upper back 3 years ago. She now has multiple liver and lung metastases. Molecular testing of a metastasis shows a BRAF V600E mutation. Which targeted treatment is directed at this abnormality?

   1. ATrastuzumab
   2. BCetuximab
   3. CDabrafenib with trametinib
   4. DImatinib

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   Answer: C · Dabrafenib with trametinib

   BRAF V600E keeps the MAPK pathway switched on and is found in about half of cutaneous melanomas. A BRAF inhibitor combined with a MEK inhibitor, such as dabrafenib with trametinib, gives better responses than a BRAF inhibitor alone and reduces the skin squamous cell carcinomas that BRAF inhibitors cause by paradoxical MAPK activation. Immune checkpoint inhibitors (anti-PD-1, with or without anti-CTLA-4) are the other main first-line option.

   • A: Trastuzumab targets HER2 in breast and gastric cancers.
   • B: Cetuximab blocks EGFR and is used in colorectal and head and neck cancers.
   • D: Imatinib targets KIT, which is mutated in some acral and mucosal melanomas, not BRAF.

5. Question 5 · Hard

   A 15-year-old boy has a rapidly enlarging, painless 6 cm mass in the soft tissue of the left forearm, with an enlarged axillary lymph node. Biopsy shows small round blue cells clinging to fibrous septa, with central loss of cohesion that creates spaces resembling lung alveoli. Immunohistochemistry: desmin positive, myogenin strongly and diffusely positive, CD99 negative, synaptophysin negative, and CD45 (LCA) negative. Which translocation is most likely present?

   1. At(2;13) PAX3::FOXO1
   2. Bt(12;16) FUS::DDIT3
   3. Ct(11;22) EWSR1::FLI1
   4. Dt(X;18) SS18::SSX

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   Answer: A · t(2;13) PAX3::FOXO1

   The panel first places the tumour among the small round blue cell tumours: CD45-negative excludes lymphoma, synaptophysin-negative excludes neuroblastoma, CD99-negative argues against Ewing sarcoma, and desmin with myogenin shows skeletal muscle differentiation. An alveolar pattern in an adolescent's limb with strong, diffuse myogenin is alveolar rhabdomyosarcoma, which usually carries t(2;13) PAX3::FOXO1 or, less often, t(1;13) PAX7::FOXO1. Fusion-positive tumours have a worse prognosis than embryonal rhabdomyosarcoma, and early nodal spread is common.

   • B: FUS::DDIT3 defines myxoid liposarcoma in adults.
   • C: EWSR1::FLI1 defines Ewing sarcoma, which is CD99-positive and myogenin-negative.
   • D: SS18::SSX defines synovial sarcoma, a spindle-cell tumour without myogenin.

6. Question 6 · Hard

   A 59-year-old man has had abdominal fullness for 6 months. CT shows an 18 cm mostly fatty retroperitoneal mass with a few thick septa, displacing the right kidney. The resected tumour is yellow and lobulated; histology shows mature-looking adipocytes that vary in size, with scattered enlarged, hyperchromatic stromal cells in fibrous septa. Which test best confirms the diagnosis?

   1. AImmunostaining for S-100 protein
   2. BImmunostaining for desmin
   3. CRT-PCR for FUS::DDIT3 fusion
   4. DFISH for MDM2 amplification

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