Spontaneously ruptured breast metastasis from renal cell carcinoma 20 years post-nephrectomy: a case report and literature review.

Background: Breast metastases from extramammary malignancies are rare, and those originating from renal cell carcinoma (RCC) are exceptionally uncommon. These lesions often follow an indolent course, delaying recognition until acute, life-threatening complications such as hemorrhagic rupture occur. The lack of standardized management guidelines further impedes timely intervention. Case presentation: An 88-year-old woman with a history of radical nephrectomy for clear cell RCC 20 years prior presented with active hemorrhage from a spontaneously ruptured right breast mass. Two years earlier, a 2.5 × 1.5 cm nodule (BI-RADS 3) had been detected but managed conservatively without biopsy, gradually enlarging over the following two years. On admission, physical examination revealed a large, tender mass (∼6.5 × 6 × 7.5 cm) with skin erythema, ulceration, and active bleeding. CT demonstrated the breast mass and revealed two additional imaging-suspected lesions: a right pulmonary nodule and a right adrenal mass. After hemodynamic stabilization, right simple mastectomy was performed, achieving definitive hemostasis. Histopathology and immunohistochemistry (CAIX+, PAX-8+, vimentin+; GATA-3-, GCDFP-15-, ER-, PR-) confirmed metastatic clear cell RCC. The patient declined systemic therapy. At 30-month telephone follow-up, she reported no symptomatic local recurrence or new symptoms; however, no postoperative imaging was performed to confirm this. Conclusion: This case illustrates a critical two-stage progression of breast metastasis from RCC-indolent growth followed by rapid enlargement and hemorrhagic rupture. It underscores that while a BI-RADS 3 lesion in an RCC survivor may be managed with standard short-interval imaging, any interval enlargement or morphological change should prompt a lower threshold for tissue confirmation. An IHC panel (PAX-8/CAIX positivity with negative breast-specific markers) is essential for confirming metastatic RCC. The absence of postoperative imaging in this case-with follow-up limited to symptom-based telephone assessment-highlights the critical importance of radiological surveillance to objectively evaluate disease status.