A 71-year-old woman has a well-circumscribed 3 cm breast lump. Histology shows clusters of bland tumor cells floating in large pools of extracellular mucin separated by fibrous septa, with mucin comprising more than 90% of the tumor volume. ER and PR are strongly positive, HER2 negative. Which feature best characterizes this entity?

• A Low incidence of axillary node involvement and excellent prognosis among breast carcinomas ✓
• B High rate of lymph node metastasis and poor 5-year survival compared to ductal NST
• C Frequent BRCA1 germline mutations explaining its occurrence in elderly women
• D Uniformly triple-negative phenotype with basal-like gene expression

Explanation

Pure mucinous (colloid) carcinoma, defined by abundant extracellular mucin in over 90% of the tumor, occurs in older women, is typically luminal (ER and PR positive), and has one of the best prognoses of any breast carcinoma subtype because the copious mucin matrix limits access of tumor cells to lymphatics, so nodal spread is infrequent. It is unrelated to BRCA1, which predisposes to high-grade triple-negative cancers, ruling out C. Its favorable biology contradicts B, and its hormone receptor positivity excludes D.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.