Introduction: Glycogen-rich clear cell carcinoma (GRCC) of the breast is a rare variant of primary breast carcinoma that is characterized by carcinoma cells containing an optically clear cytoplasm and intracytoplasmic glycogen. An ongoing debate exists whether it harbors aggressive clinical features. Case Report: The authors report the case of a 41-year-old Greek female patient, who had noticed a lump in the upper inner quadrant of the left breast. The patient underwent a left radical mastectomy with sentinel lymph node excisional biopsy and the histopathological diagnosis revealed a pT3pN0cM0R0 luminal-HER2 GRCC invasive carcinoma of the breast. Although the patient received aggressive multimodal adjuvant chemoradiation, as well as hormone therapy, she recurred 31 months after the operation with cervical, supraclavicular, and mediastinal lymph node metastasis on the left side. Conclusions: The biological behavior of GRCC is difficult to predict. According to the presented data, a gap in therapy might exist regarding the treatment of GRCC. Larger studies should be performed in order to refute or confirm this hypothesis.