Isolated Renal Metastasis Mimicking Primary Renal Cell Carcinoma

The majority of isolated renal masses are found to be primary renal cell carcinoma. However, in some rare cases, such a presentation can reveal an underlying metastasis of an occult neoplasm elsewhere. We report here a case of papillary thyroid carcinoma that presented as an isolated renal mass in an 80-years-old woman with no history of thyroid cancer. The patient underwent a radical nephrectomy by laparoscopy after a negative extension work-up for a suspected primary RCC. Pathology later confirmed it as a metastasis of papillary thyroid carcinoma, prompting a thyroid biopsy, which came back positive. PET scan showed no other metastasis, prompting total thyroidectomy and adjuvant 200mCi of I131. As of today, she remains in complete remission. In the presence of a large isolated renal mass, clinicians should remain suspicious of potential metastatic disease as it can allow for early detection and management of the primary neoplasm.