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Although renal cell carcinoma (RCC) is a frequent recipient tumor, metastasis from breast carcinoma to RCC is extremely rare. A 64-year-old woman with long-standing hormone receptor\u2013positive breast carcinoma presented with a 23-mm enhancing right renal mass. Robot-assisted partial nephrectomy revealed clear cell RCC with intratumoral nests of metastatic breast carcinoma. Immunohistochemistry revealed a reciprocal staining profile: RCC cells were positive for PAX8 and CA9, whereas metastatic breast carcinoma cells expressed CK7 and GATA3 with weak ER positivity. Clear cell RCC may serve as a recipient tumor for breast carcinoma metastasis, emphasizing that TTM should be considered in the differential diagnosis of renal masses in patients with a history of breast carcinoma, even when imaging findings are consistent with conventional RCC.<\/jats:p>","DOI":"10.1007\/s13730-026-01156-9","type":"journal-article","created":{"date-parts":[[2026,7,28]],"date-time":"2026-07-28T04:49:31Z","timestamp":1785214171000},"update-policy":"https:\/\/doi.org\/10.1007\/springer_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Tumor-to-tumor metastasis of breast carcinoma to clear cell renal cell carcinoma: a rare case with a review of the literature"],"prefix":"10.1007","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-6307-032X","authenticated-orcid":false,"given":"Nobuyuki","family":"Nakajima","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hiroshi","family":"Kajiwara","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Kenta","family":"Okutsu","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Toshiki","family":"Sakemura","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Haruka","family":"Ikoma","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tatsuya","family":"Otaki","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Soichiro","family":"Yuzuriha","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Takato","family":"Uchida","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Tatsuya","family":"Umemoto","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yoshiaki","family":"Kawamura","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yohei","family":"Masugi","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sunao","family":"Shoji","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"297","published-online":{"date-parts":[[2026,7,28]]},"reference":[{"issue":"3","key":"1156_CR1","doi-asserted-by":"publisher","first-page":"635","DOI":"10.1002\/1097-0142(196809)22:3<635::AID-CNCR2820220320>3.0.CO;2-O","volume":"22","author":"LV Campbell Jr","year":"1968","unstructured":"Campbell LV Jr, Gilbert E, Chamberlain CR Jr, Watne AL. 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