Background: Primary myoepithelial carcinoma (MEC) of the breast is exceptionally rare and diagnostically challenging. The role of 18F-FDG PET/CT in its evaluation is not well defined.

Case presentation: A 52 year old woman with history of right breast ductal carcinoma, post MRM and chemo-radiation therapy followed by tamoxifen 14 years back, had now presented with a 1.8 x 1.6 cm, firm, non tender, mobile left breast lump and a right neck lump.USG guided FNAC of the right lobe lesion of thyroid gland revealed metastatic carcinoma. Core biopsy of the breast lesion showed a biphasic neoplasm with predominant malignant myoepithelial differentiation. Preoperative 18F-FDG PET/CT demonstrated high grade FDG uptake confined to the primary tumor (SUVmax 9.8) in the left breast with high grade FDG avid contralateral ( right) thyroid lesion, infraclavicular lymph node and moderate grade FDG avid subcentimetric right internal mammary lymph node. Histopathology and immuno-histochemistry of breast lesion confirmed myoepithelial carcinoma; the myoepithelial component stained strongly for p63, S100, CK5/6, and lacked ER/PR/HER2 expression; Ki-67 was ~20%. Subsequently patient was planned for systemic chemotherapy and radiation therapy and has received 2 cycles of chemotherapy so far.

Conclusions: Breast MEC is a rare, aggressive neoplasm requiring meticulous histopathologic/IHC work up. 18F-FDG PET/CT can complement conventional imaging by providing whole body staging and a quantitative baseline for follow up in selected cases. Multidisciplinary discussion remains essential given limited high level evidence.