Uterine intra‐leiomyoma metastasis originating from primary breast cancer: A rare entity

Metastasis to the female genital tract from extragenital primaries is uncommon, with breast and gastrointestinal malignancies representing the predominant sources. Uterine involvement accounts for fewer than 10% of genital tract metastases and most frequently occurs in the setting of disseminated disease with concomitant ovarian involvement. Invasive lobular carcinoma (ILC), despite comprising only 5%-20% of breast malignancies, accounts for over 80% of breast cancer metastases to the female genital tract, a predilection attributed to loss of E-cadherin expression-facilitating tumor cell detachment and hematogenous dissemination-and its diffuse infiltrative growth pattern. Metastasis to uterine leiomyomas is exceptionally rare, with approximately 30 cases reported to date. The underlying pathophysiologic mechanism is postulated to involve the hormonally enriched microenvironment of leiomyomas, wherein tissue concentrations of estrogen and progesterone receptors significantly exceed those of the surrounding myometrium, thereby conferring preferential tropism for circulating hormone receptor-positive breast carcinoma cells. Supporting this, 92.3% of reported cases were estrogen receptor positive. Concurrent lymphatic and hematogenous dissemination pathways are implicated based on patterns of organ involvement, with isolated uterine metastasis in the absence of ovarian disease favoring hematogenous spread. We report a case of metastatic invasive ductal/lobular carcinoma (ER+/PR+/HER2-) infiltrating a uterine leiomyoma, identified incidentally on histopathologic examination six years after primary treatment, in an asymptomatic African American woman undergoing hysterectomy for pelvic organ prolapse-representing, to our knowledge, the first such case reported in an African American patient. Immunohistochemical profiling confirmed breast origin and receptor concordance with the primary tumor.