A 36-year old female was diagnosed with a breast infiltrating duct carcinoma, NOS, G2, luminal B HER2-neg, metastatic to the lymph nodes, lungs, liver and bones. She received ribociclib, fulvestrant and LHRH analog for 15 months with partial remission. For personal reasons the patient interrupted therapy for 4 months, but reported afterwards due to rapid progression. A core-biopsy revealed no presence of usual infiltrating duct carcinoma, but unequivocal choriocarcinomatous differentiation with mononuclear cytotrophoblast-like cells with hyperchromatic nuclei and multinucleated syncytiotrophoblast-like giant cells (fig. 1) and strong cytoplasmatic immunoreactivity for β-HCG (fig. 2). Pathologist suggested either a rare variant of invasive breast carcinoma with a choriocarcinomatous pattern or metastatic choriocarcinoma to the breast. Metastatic progression was seen; pregnancy, as well as primary choriocarcinoma were excluded; total β-HCG was 80,000 mU/ml. The patient received cisplatin plus etoposide with moderate clinical improvement and rapid decrease of β-HCG level. Invasive carcinoma of the breast with a choriocarcinomatous pattern is an extremely rare subtype of breast cancer listed in the WHO classification, with only few cases reported [1]. Systemic treatment was adjusted to the updated histopathological diagnosis. No optimal chemotherapy regimen is defined so far, and prognosis is unclear in advanced cases [3].

Figure 1. Core biopsy of breast carcinoma with a choriocarcinomatous pattern – both components of choriocarcinoma (cytotrophoblast-like and syncytiotrophoblast-like cells) are seen, staining H&E, x100 magnification

Figure 2. Core biopsy of breast carcinoma with choriocarcinomatous pattern – strong immunoreactivity for β-HCG in neoplasmatic cells, β-HCG immunostaining, x200 magnification

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