To investigate the clinicopathological features, diagnosis, differential diagnosis and prognosis of renal collecting duct carcinoma (CDC).

The clinical data of 3 patients with renal collecting duct carcinoma, during the period from January 2015 to November 2017, were retrospectively analyzed. 3 patients were male with age ranged from 42 to 73 years old, mean of 57.5 years. Two lesions were located in the right kidney and one in the left kidney. Clinical manifestations were hematuria, abdominal mass and waist and abdomen pain. No laboratorial abnormality was found. CT examination showed the tumor diameter ranged from 3.1 to 5.1 cm, mean 3.9 cm. The tumors located in the medullary and renal pelvis with low density or mixed density.Those tumors extended to the peripheral of the kidney, which the boundary was unclear. During enhancement CT, the uneven enhancement effect could be observed. Radical nepheroectomy was performed in all patients.

Postoperative pathological examination showed surface of incision was gray. The texture of tumor was hard. The invasive growth pattern could be noticed. Under the microscope, the tumors had small ducts and papillary structures of tubules with interstitial fibrosis and some sarcomatous differentiation. Immunohistochemical staining showed strong positive expression of vimentin, CK-L, CKpan and P504S, and positive expression of PAX-2, CK7 and EMA in different degrees. RCC, KSP, CD10, CD117, MOC-31 and TFE3 were all negative. All 3 cases were followed up from 1 to 15 months with an average of 6 months. One case was treated with chemotherapy because of extensive metastases after surgery. Chemotherapy was performed by dissolving 1 500 mg of fluorouracil in 1 000 ml of 5% normal saline and instillation. It was administered once every 10-12 hours and once a day for 5 days in one cycle. However, the outcome was poor. 1 patient died of tumor metastasis and recurrence 7 months after surgery. 1 patient had no tumor remaining after surgery.

CDC is a very rare malignant epithelial neoplasm in kidney. It has obvious clinical symptoms, strong invasive pattern and poor prognosis. Imaging and ultrasonography only play an auxiliary role in diagnosis. CDC's unique histopathology is the main basis of diagnosis and differential diagnosis.

Kidney neoplasms; Collecting duct carcinoma; Immunohistochemistry; Pathological diagnosis and prognosis