Glycogen-rich Clear Cell Carcinoma of the Breast: A Comprehensive Review.

Glycogen-rich clear cell carcinoma (GRCC) is a very rare form of primary breast cancer (<0.1% of all breast cancers). It is characterized by the presence of neoplastic cells with a glycogen-abundant clear cytoplasm (the Periodic Acid Schiff-positive, diastase-sensitive). The expression of steroid receptors (estrogen and progesterone receptors) has been variably reported (35% to 100% of the cases), whereas most studies reported low human epidermal growth factor receptor 2 positivity in GRCC. High androgen receptor positivity without androgen receptor splice variant-7 was reported in one recent study. Although sparse, the preliminary theranostic data on GRCC indicate the potential of targeted treatments in selected cases (antiandrogen, PIK3CA, and immune checkpoint inhibitors). Because of its rarity, the prognosis for GRCC patients remains controversial. Herein, we comprehensively appraise the epidemiological, morphologic, molecular, and clinical characteristics of this rare mammary malignancy.