To investigate the clinicopathologic characteristics, diagnostic features and prognosis of primary renal neuroendocrine carcinoma (NEC).

The clinicopathologic data of eight cases of renal NEC was collected from January 2008 to December 2017 from Affiliated Hospital of Qingdao University. Immunohistochemical staining was performed, and follow-up information was analyzed, and the relevant literature reviewed.

The patients′ mean age at diagnosis was 45 years (range, 27-66 years); five were women, and three were men. The tumors located on the left side in five patients, and on the right side in three. Five cases were detected incidentally, and three patients presented with loin pain. Microscopically, these cases included five well-differentiated NECs (three carcinoids, two atypical carcinoids), two small cell NECs, and one large cell NEC according to the World Health Organization classification of 2016. The tumors infiltrated the renal capsule in six cases. Necrosis was found in five cases. Vascular invasion with tumor emboli was seen in three cases. Lymph node metastasis was identified in one case. Immunohistochemically, the expression rates of neuroendocrine markers CD56, chromogranin A (CgA) and synaptophysin (Syn) were 6/8, 4/8, and 8/8 respectively. Some of the NECs were positive for epithelial markers CKpan (6/8, with three cases showing focal positivity) and CAM5.2 (4/8) of variable degrees. The Ki-67 proliferation index was≤3% in the carcinoids; ≥50% in the small cell carcinoma and large cell carcinoma; and 5% and 8% for the two cases of atypical carcinoid, respectively. All cases were negative for EMA, CK7, CA9, CD10, CD117, PAX2, PAX8, WT1, p63, S-100 and TTF1. Three patients (two with small cell carcinoma and one with large cell carcinoma) died of extensive metastases at 3 months, 4 months and 9 months after operation, while five patients were well, without recurrence or distant metastasis for follow-up period of one to nine years.

Primary renal NEC is rare. Carcinoid is the most common histological type. The pathomorphological features and neuroendocrine markers (CD56, CgA, Syn), epithelial markers (CKpan, CAM5.2) and nephrogenic markers (PAX2, PAX8) are important for the diagnosis. Renal carcinoid tumors are indolent and prone to early metastasis, but are associated with prolonged survival. The small cell renal cell carcinoma and large cell carcinoma are highly malignant renal tumors with poor prognosis and short survival.

Kidney neoplasms; Neuroendocrine tumors; Immunohistochemistry; Prognosis