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Lobular Breast Cancer — SCE Medical Oncology MCQ

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HardBreast CancerLobular Breast CancerSCE Medical Oncology

A woman previously treated for ER-positive invasive lobular breast cancer develops peritoneal thickening, bilateral hydronephrosis and an ovarian mass. Biopsy shows discohesive signet-ring-like cells. Which immunophenotype most strongly supports metastatic lobular breast carcinoma over a Müllerian primary?

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Correct answer: C — GATA3 positive, ER positive, PAX8 negative, with loss of E-cadherin

Explanation lettering: E = shown as A · A = shown as B · B = shown as C · C = shown as D · D = shown as E

B is correct. Invasive lobular carcinoma characteristically spreads in an infiltrative fashion to peritoneum, retroperitoneum, gastrointestinal and gynaecological sites. GATA3 and ER support breast origin, PAX8 negativity argues against Müllerian origin, and E-cadherin loss supports lobular phenotype. A is typical of high-grade serous Müllerian carcinoma. C supports lower gastrointestinal origin. D supports pulmonary adenocarcinoma. E favours mesothelial differentiation. No single stain is perfectly specific, so morphology, the original tumour and a panel including breast and site-specific markers must be integrated.

Reference: Infiltrative metastatic invasive lobular breast carcinoma review: https://pmc.ncbi.nlm.nih.gov/articles/PMC8665916/