Papillary renal cell carcinoma Papillary renal cell carcinoma accounts for approximately 10-15% of all patients with kidney cancer. The majority of tumor tissue in this subtype of renal cell carcinoma is papillary, sometimes with tubular and parenchymal structures. The tumor papillae include a microtubular core and are often accompanied by edema or glassy connective tissue. Papillary renal cell carcinoma can be divided into two histologic subtypes based on histologic criteria and differences in gene expression profiles. type I papillary renal cell carcinoma is generally less malignant and has a good prognosis. type II papillary renal cell carcinoma is generally more malignant and has a poor prognosis. Smoldering renal cell carcinoma Smoldering renal cell carcinoma accounts for approximately 5% of all patients with renal cell carcinoma. Part of the reason for the favorable outcome of this cancer may be related to the fact that patients are usually in the early stages. In addition, the prognosis for high-grade and advanced-stage suspicious renal cell carcinoma is generally poor. Renal collecting duct carcinoma Renal collecting duct carcinoma was previously known as Bellini’s duct carcinoma. Renal collecting duct carcinoma is a very rare lesion, accounting for less than 1% of the total number of patients with renal cell carcinoma. It usually occurs in the renal medulla, which distinguishes it from other subtypes of renal cell carcinoma. The cells of renal collecting duct carcinoma usually have high-grade cellular characteristics. Medullary carcinoma is another highly malignant subtype of renal cell carcinoma with morphologic features similar to those of collecting duct carcinoma. However, renal medullary carcinoma typically develops in young patients and is associated with sickle cell anemia. Immunohistochemistry negative for INI1 (SMARCB1) and positive for OCT3/4 can help distinguish renal medullary carcinoma from renal collecting duct carcinoma. Xp11.2 translocation-associated renal cell carcinoma Xp11.2 translocation-associated renal cell carcinoma is a very rare and difficult to diagnose renal cell carcinoma. Even when diagnosed at an advanced stage, Xp11.2 translocation-associated renal cell carcinoma in children and adolescents is usually not very malignant. In contrast, Xp11.2 translocation-associated renal cell carcinoma in adults is more clinically aggressive and is associated with lymph node metastasis in advanced stages (stage III or IV). Sarcomatoid differentiation-associated renal cell carcinoma Sarcomatoid differentiation of renal cell carcinoma is not a histologic subtype, but a pathologic feature. Expression of paired cassette gene 8 (PAX8) by spindle cells is one of the diagnostic indicators of poorly differentiated renal cell carcinoma. Sarcomatoid differentiation features of renal cell carcinoma are independent indicators of clinical tumor progression and poor prognosis. The incidence of sarcomatoid differentiation in renal cell carcinoma is approximately 5%.