Case 23

A 63-year-old female with a 3.2 cm mass at left breast.

What's the diagnosis?

A: Invasive ductal carcinoma

B: Invasive lobular carcinoma

C: Histiocytes

Answer

The correct answer is B. This is a classic invasive lobular carcinoma by the single file pattern, invading and dissecting adipose tissue. Classically, ILC showed ER+, PR+, and HER2-, 83% as luminal A subtype. Of note, per WHO: "about 15% of ILCs (and most ductulolobular cancers) do express E-cadherin, so positive staining should not be used to reclassify a lobular lesion as IBC-NST." Coexist of LCIS or ALH can be helpful.

Reference: https://tumourclassification.iarc.who.int/chaptercontent/32/19

Case credit: UCSD Pathology

Author: Wangpan Jackson Shi, MD