Neuroendocrine tumors (NETs) are uncommon tumors that exhibit a wide range of differentiation and biological behavior. NETs can arise from any tissue or organ, including organs that do not normally contain neuroendocrine cells. NETs embrace a large spectrum of diseases rarely originating from the kidney (2); they include well-differentiated NET (carcinoid), well-differentiated neuroendocrine carcinoma, poorly differentiated neuroendocrine carcinoma and small cell carcinoma. Renal carcinoids are typically slow-growing tumors with a variable clinical course. We herein report a rare case of well-differentiated NET (carcinoid) in a 17-year-old male along with the immunohistochemical features and a review of the literature.
A 18-year-old male presented with dull pain in the left flank since 9 months. The abdominal examination revealed a big palpable mass in the left abdomen; CT scan showed a huge cystic tumor occupying the entire left part of the abdominal cavity arising from the left kidney with maximum diameter > 30 cm without regional node involvement and distant metastasis.
US-guided percutaneous biopsy of the neoplasm was inconclusive and the patient underwent surgical removal of a large renal tumor displacing all the surrounding organs in absence of infiltrative growth pattern. The mass was excised by blunt dissection from the kidney allowing to preserve a large amount of healthy renal parenchyma.
Gross examination revealed a brown coloured cystic mass with large haemorragic areas, apparently surrounded by a fibrous capsule.
On microscopic examination there was absence of necrosis and mitotic figures were scant (<2/10 HPF). Immunohistochemically, these tumor cells were diffusely positive for chromogranin, synaptophysin, vimentine, CK8/18 and negative for GFAP, pS100, RCC, PAX-8, WT-1 and CK-7. Ki-67 index was nearly 2%. Thus, a diagnosis of well-differentiated NET was given.
NETs are most commonly seen in the gastrointestinal tract, less frequently in the respiratory system and sporadically in parenchymal organs such as the liver. Primary NETs of the kidney are extremely rare. They can occur in both the renal parenchyma and the renal pelvis.
The pathogenesis of primary NETs of the kidney is still controversial. Neuroendocrine cells have been identified in the renal pelvis but not in the normal renal parenchyma. Different theories support the fact that NETs arise from primitive totipotential stem cells that subsequently differentiate in a neuroendocrine direction. Several mechanisms have been used to explain the origin of such tumors, including metastasis from an occult primary tumor site to the kidney, activation of aberrant gene sequences in a totipotential stem cell line that differentiates into aberrant NET cells, and concurrent renal congenital abnormalities. Some authors think that the tumors arise from neuroendocrine cells occurring in the mucosa of the renal pelvis in intestinal metaplasia.
In 2010, the WHO has proposed a classification system for renal carcinoid tumors that is similar to that of the carcinoid tumors of other organs. They classified neuroendocrine neoplasms into NET-well differentiated grade 1, NET-well differentiated grade 2, NEC-poorly differentiated grade 3 (small and large cell type), mixed adenoneuroendocrine carcinoma, hyperplastic, and preneoplastic lesions. This classification differentiates between NETs and neuroendocrine carcinomas. The proliferation index (Ki-67, MIB-1), angioinvasion, and mitoses are important factors in this classification.
Well-differentiated NET (carcinoid) of the kidney are rare with 4 cm. This could be due to the vacuous nature of the retroperitoneal space as kidneys are essentially retroperitoneal organs.
There is no clear correlation between the histologic features of the disease and prognosis and tumor necrosis is not a predictor of prognosis. Metastatic workup must always be done to rule out the possibility of metastasis from an occult tumor elsewhere when a clinical diagnosis of renal carcinoid is made. Long-term follow-up care is essential because of the prolonged course of disease despite metastasis. The clinical course of renal carcinoid is difficult to predict because of the rarity of the condition; however, it is largely believed to have an indolent course
The current recommended management for primary renal carcinoid tumors includes radical nephrectomy with surveillance and surgical removal of any subsequent metastases. Even partial nephrectomy is recommended. The average follow-up time is 20 months with 73.1% of patients without evidence of disease after surgical treatment which suggests that surgical treatment is curative., Liver metastasis can be treated with open resection or with minimally invasive ablative procedures. Metastatic renal carcinoid has been noted to be resistant to chemotherapy.
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