Spontaneous regression of multiple pulmonary nodules in a patient with unclassified renal cell carcinoma following laparoscopic partial nephrectomy: A case report.

Spontaneous regression of metastatic renal cell carcinoma (RCC) is rare, but well-documented in clear cell RCC. However, there are no reports on spontaneous regression of unclassified RCC. Since the radiological findings of pulmonary infarcts and inflammatory pseudotumors are similar to those of metastases from RCC, a definitive diagnosis is difficult without performing a histological examination. A 56-year-old woman underwent medical examination by a physician. An abdominal computed tomography (CT) scan revealed a 22-mm mass with a cystic area in the right kidney, as well as multiple enlarged lymph nodes in the common iliac, external iliac and groin areas, bilaterally. A chest CT revealed multiple pulmonary nodules bilaterally, the largest measuring 15 mm. Since the right renal tumor was suspected to be an RCC, laparoscopic partial nephrectomy was performed. The final pathological diagnosis of the renal tumor was unclassified RCC. One month following surgery, a CT scan revealed spontaneous regression of the pulmonary nodules. We herein present a rare case of spontaneous regression of pulmonary nodules in a patient with unclassified RCC following laparoscopic partial nephrectomy. To the best of our knowledge, this is the first case of spontaneous regression in unclassified RCC.