A 71-year-old woman was diagnosed with sigmoid colon cancer with lung metastasis. One month after diagnosis, she underwent sigmoid colon resection with D3 lymph node dissection. Preoperative contrast-enhanced computed tomography (CT) had revealed a tumor in the left kidney, but this tumor was not prioritized for treatment. The definitive diagnosis was sigmoid colon cancer (pT3N0M1), and the patient received chemotherapy with mFOLFOX6 (oxaliplatin [85 mg/m2], levofolinate [200 mg/m2], and fluorouracil [400 mg/m2 bolus followed by 2400 mg/m2 over 12 cycles]) plus bevacizumab (Avastin; Genentech, South San Francisco, CA, USA [5 mg/kg]). The patient achieved a partial response with chemotherapy; however, the chemotherapy was discontinued at the patient’s request after two cycles. One year after surgery, she was diagnosed with advanced lung metastasis and underwent robot-assisted right upper lobectomy in another hospital. Contrast-enhanced CT obtained 2 years after the initial surgery revealed that the previously noted left renal tumor had become enlarged to an approximate size of 6 cm, and it exhibited internal heterogeneous contrast accumulation (Fig. 1a, b). 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) revealed two sites of strong signal accumulation in the renal tumor (Fig. 2a, b), which differed from the findings observed 1 year earlier. Laboratory tests revealed the following: white blood cell count, 4800/µL (neutrophil count, 2230/µL); hemoglobin, 12.8 g/dL; platelet count, 213,000/µL; creatinine, 0.62 mg/dL; estimated glomerular filtration rate, 71.2 mL/min/1.73 m2; calcium, 9.7 mg/dL; C-reactive protein, 0.17 mg/dL; carcinoembryonic antigen (CEA), 366.6 ng/mL (≤ 5.0 ng/mL); and CA19-9, 2.7 U/mL (≤ 37 U/mL). The imaging results and elevated CEA suggested that the left renal tumor was either a primary renal cancer or a left renal metastasis of sigmoid colon cancer. Therefore, the patient underwent laparoscopic partial left nephrectomy 1 month later.

Contrast-enhanced computed tomography image showing a tumor with internal heterogeneous contrast accumulation in the left kidney. a Before and b after intratumoral metastasis of sigmoid colon cancer to renal cell carcinoma

18F-fluorodeoxyglucose-positron emission tomography images. a No accumulation was present before intratumoral metastasis. b Two strong accumulations in the left kidney were observed after intratumoral metastasis

The patient was placed under general anesthesia in the right lateral recumbent position, and a transabdominal approach was used. A camera port was placed on the outer edge of the rectus abdominis muscle two finger widths cephalad to the umbilicus, and a 12-mm port was placed 7 cm cephalad to the camera port. After dissection of the adhesions between the abdominal wall and mesentery, a 12-mm port was placed 7 cm lateral to the camera port, and an assistant 12-mm port was placed caudal to the camera port. The tumor was located in the suprarenal pole lateral to the kidney, and tumor resection was performed from the ventral to dorsal side. The operative duration was 4 h 30 min, and the pneumoperitoneum time was 3 h 42 min. The total blood loss was 50 mL, the ischemia time was 18 min, and the excised tumor was 75 × 65 × 40 mm in size.

Histopathologic examination revealed that the tumor was a chromophobe renal cell carcinoma (expansive type, 70 mm in maximum tumor diameter, Grade 2; WHO/ISUP grading system atypia classification, Grade 2; Fuhrman classification, LyX, VX, pT2a, INFa, eg, fc1, imX, rc-inf0, rp- inf0, s-inf0) (Fig. 3). In addition, multiple colon cancer metastatic lesions were observed inside the renal tumor, including a mass measuring 30 mm. Histologic examination of the intratumoral metastatic lesions revealed highly to moderately differentiated tubular adenocarcinoma (Fig. 4). Immunostaining (Fig. 5) revealed AE1/AE3 positivity in the renal carcinoma, colon carcinoma, and normal renal tubules; CK7 positivity in the renal carcinoma and normal renal tubules; CK20 positivity only in the colon carcinoma; and c-kit and colloidal iron positivity in the chromophobe renal cell carcinoma. By contrast, CA9 immunostaining was negative throughout. Based on these results, the definitive diagnosis of the renal tumor was chromophobe renal cell carcinoma. The central portion of the tumor was consistent with the histologic features of the previously resected sigmoid colon cancer: this region was CK7-negative and CK20-positive by immunostaining, confirming the diagnosis of intratumoral metastasis of sigmoid colon cancer to chromophobe renal cell carcinoma.

Gross appearance of the resected renal tumor. Arrows indicate colon cancer metastases

Hematoxylin/eosin staining of chromophobe renal cell carcinoma (yellow arrows) with intratumoral metastatic carcinoma (red arrows). Magnification, 100 × 

Immunostaining of chromophobe renal cell carcinoma (yellow arrows) with intratumoral metastatic carcinoma (red arrows). a CK7. b CK20. c c-kit. d Colloidal iron. Magnification of all panels, 100 × 

Postoperative laboratory tests revealed the following: creatinine, 0.70 mg/dL; estimated glomerular filtration rate, 62.3 mL/min/1.73 m2; and CEA, 40.4 ng/mL. Multiple lung metastases were observed 2 months after the partial nephrectomy (PN), and chemotherapy with bevacizumab plus SOX (capecitabine + oxaliplatin [130 mg/m2] + S-1 [100 mg]) was initiated for the lung metastasis of colon cancer. CT showed no renal recurrence, but multiple lung metastases and a new bone metastasis in the left ischium were observed. The patient declined further treatment, and chemotherapy was, therefore, discontinued. Six months after PN, brain metastasis appeared. Radiotherapy for the brain metastasis was being performed at the time of this writing.