When Breast Cancer Meets the Uterus: A Quantitative Review of 105 Cases Spanning Four Decades

Background and Objectives: Uterine metastasis from breast carcinoma is rare but poses substantial diagnostic and therapeutic challenges. Invasive lobular carcinoma (ILC) demonstrates a documented predilection for unusual metastatic patterns including the female genital tract, while tamoxifen-associated endometrial pathology may complicate diagnosis in breast cancer survivors. Materials and Methods: We performed a structured PubMed/MEDLINE and Google Scholar search (1980-2025) for cases with histologically confirmed breast primary and uterine involvement; a pooled analysis of demographic, histological, molecular, and clinical variables was performed. Results: 105 individual cases were identified. ILC accounted for 58.0% of histologically classified cases despite representing only 10-15% of breast cancers. Endometrial involvement was present in 68.6%, myometrial in 25.7%, and cervical in 26.7%. Tamoxifen exposure was strongly associated with polyp-substrate metastasis (29.3% vs. 4.7%; Fisher's exact p = 0.0009; OR 8.41, 95% CI 2.20-32.14). Abnormal uterine bleeding was the dominant presentation (68.1%); 19.8% were asymptomatic. Median latency was 36 months (range from 24 months before to 360 months after the breast cancer diagnosis). Conclusions: Uterine metastasis from breast carcinoma is dominated by invasive lobular histology and frequently involves tamoxifen-associated polyps. A combined immunohistochemical panel (GATA3, TRPS1, E-cadherin, hormone receptors, PAX8) is essential for distinguishing metastatic disease from primary uterine pathology. Endometrial sampling should be considered with a low threshold in breast cancer survivors with abnormal uterine bleeding, and breast imaging is warranted when discohesive cells are encountered without a known breast primary. These proportions describe the published case literature rather than population-based prevalence; because the evidence is limited to case reports and small series, they should not be read as the true frequency of uterine involvement among women with breast cancer.