Kidney tumors can either be benign (non-cancerous) or malignant (cancerous). There are certain tumors that are classified as atypical (uncertain or unspecified behavior) meaning that some behave in a benign manner, or some behave in a malignant manner. A majority of the tumors diagnosed via lab studies (biopsy) are benign.

The World Health Organization (WHO) is an authoritative body that compiles, prepares, and publishes histological and molecular classification of tumors, via their Blue Books, based on research inputs from experts worldwide. These reference books chiefly aid in global cancer research, provide gold standards for tumor diagnosis, and help in treating cancer patients.

According to the WHO Classification of Urinary and Male Genital Tumors (2019), 5th Ed., Vol. 8, benign and malignant tumors of the kidney are classified in the following manner:

Tumors of the kidney:

• Renal cell tumors
  • Renal cell tumors
• Clear cell renal tumors
  • Clear cell renal cell carcinoma: A type of renal cell carcinoma (kidney cancer) that develops from the renal cortex and more commonly seen in older adults. It is a malignant tumor that develops due to an abnormality within the tissue lining in the tubules of the kidney
  • Multilocular cystic renal neoplasm of low malignant potential: A rare type of renal cell carcinoma (kidney cancer) that develops from the renal cortex and more commonly affecting middle-aged adults. It is a malignant tumor that develops due to an abnormality within the tissue lining in the tubules of the kidney
• Papillary renal tumors
  • Renal papillary adenoma: It is a tumor of the kidney that is generally diagnosed in adults. It is usually considered to be a low-grade neoplasm
  • Papillary renal cell carcinoma: A type of renal cell carcinoma (kidney cancer) that develops from the renal cortex and usually seen in adults. It is a malignant tumor that develops due to an abnormality within the tissue lining in the tubules of the kidney, bladder, ureter, or urethra
• Oncocytic and chromophobe renal tumors
  • Oncocytoma of the kidney: It is a benign solid tumor of the kidney that is generally diagnosed in middle-age and older adults. In many cases, the tumors are found incidentally while examining the individual for other medical conditions.
  • Chromophobe renal cell carcinoma
  • Other oncocytic tumors of the kidney
• Collecting duct tumors
  • Collecting duct carcinoma: It is a rare, aggressive type of renal cell carcinoma (a form of kidney cancer) that generally affects adult males and females. It is a malignant tumor that develops due to an abnormality within the tissue lining in the collecting ducts of the kidney
• Other renal tumors
  • Clear cell papillary renal cell tumor
  • Mucinous tubular and spindle cell carcinoma: It is a rare type of renal cell carcinoma (kidney cancer) of low-grade malignancy. It is observed in a wide age range of individuals, typically in women
  • Tubulocystic renal cell carcinoma: A rare type of renal cell carcinoma (kidney cancer) affecting adults. It is a malignant tumor that develops within the tissue lining in the collecting ducts of the kidney. The tumor consists of tubules, microcysts, and macrocysts, when examined under the microscope by a pathologist
  • Acquired cystic disease-associated renal cell carcinoma
  • Eosinophilic solid and cystic renal cell carcinoma
  • Renal cell carcinoma NOS
• Molecularly defined renal carcinomas
  • TFE3-rearranged renal cell carcinomas
  • TFEB-rearranged renal cell carcinomas
  • ELOC (formerly TCEB1)-mutated renal cell carcinoma
  • Fumarate hydratase-deficient renal cell carcinoma
  • Succinate dehydrogenase-deficient renal cell carcinoma
  • ALK-rearranged renal cell carcinomas
  • SMARCB1-deficient renal medullary carcinoma
• Metanephric tumors
  • Metanephric adenoma: It is a rare benign tumor consisting of epithelial cells. It arises from the distal nephron or collecting ducts of the kidney. The tumor is seen in a wide age range of individuals
  • Metanephric adenofibroma: It is a rare benign tumor of the kidney consisting of epithelial and stromal cells. The tumor is mostly seen among the younger populations (children and adolescents)
  • Metanephric stromal tumor: It is a benign tumor of kidney consisting of stromal cells. The tumor is seen among children and sometimes in teens
• Mixed epithelial and stromal renal tumors
  • Mixed epithelial and stromal tumor of the kidney

Renal mesenchymal tumors

• Adult renal mesenchymal tumors
  • Classic angiomyolipoma / PEComa of the kidney: It is stated to be among the most common benign tumor of the kidney. The tumor may be present in the cortex or medulla of the kidney. It may be associated with a syndrome (tuberous sclerosis) in some cases
  • Epithelioid angiomyolipoma / epithelioid PEComa of the kidney
  • Renal hemangioblastoma
  • Juxtaglomerular cell tumor: It is a mostly benign kidney tumor that secretes renin. The secretion of renin leading to its increased level in blood, results in high blood pressure (hypertension)
  • Renomedullary interstitial cell tumor: It is a common benign tumor of the kidney that is usually discovered incidentally. The tumor is seen in a wide age range of adults
• Pediatric renal mesenchymal tumors
  • Ossifying renal tumor of infancy: It is a very uncommon benign tumor of childhood, usually observed within the first 24 months. The tumor is typically present in the medulla of the kidney
  • Congenital mesoblastic nephroma
  • Rhabdoid tumor of the kidney
  • Clear cell sarcoma of the kidney

Embryonal neoplasms of the kidney

• Nephroblastic tumors
  • Nephrogenic rests
  • Pediatric cystic nephroma: It is an uncommon and benign cystic tumor of kidney that is present in young children, typically boys
  • Cystic partially differentiated nephroblastoma
  • Nephroblastoma

Miscellaneous renal tumors

• Germ cell tumors of the kidney

Additional kidney tumor articles (on DoveMed) that are not part of WHO Classification of Urinary and Male Genital Tumors:

Adenocarcinoma of Renal Pelvis: It is a rare type of renal cell carcinoma (kidney cancer) that develops from the renal pelvis. It is a malignant tumor that develops due to an abnormality within the tissue lining in the pelvis of the kidney. The tumor mostly affects older adults.

Carcinoid Tumor of Kidney: It is a type of neuroendocrine carcinoma of the kidney. This malignant tumor generally affects adult males and females.

Cystic Nephroma of Kidney: It is an uncommon and benign cystic tumor that may be present in both children and adults. The tumor is usually single and typically affects only one kidney.

Diffuse Large B-Cell Lymphoma (DLBCL) of Kidney: It is a rare B-cell non-Hodgkin’s lymphoma that affects older adults. It is a common subtype of lymphoma of kidney and may be associated with autoimmune disorders and viral infections.

Fibroepithelial Polyp of Renal Pelvis: It is an uncommon benign tumor generally present in a wide range of adults. Many tumors are found incidentally while examining the individual for other medical conditions.

Glomus Tumor of Kidney: It is a mostly benign tumor that is seen among a wide age range of adults. The kidney is an uncommon location for the tumor but can be present in the cortex or medulla of the kidney.

Inflammatory Myofibroblastic Tumor of Kidney: It is a very rare, benign tumor with aggressive behavior affecting the kidney. The tumor generally develops in younger populations and may sometimes grow to large sizes.

Kidney Hemangioma: It is a rare, benign vascular tumor of the kidney that is often observed in individuals under the age of 40 years. Certain genetic syndromes may increase the risk for these tumors.

Large Cell Neuroendocrine Carcinoma of Kidney: It is a type of renal carcinoma (form of kidney cancer). The malignant tumor generally affects men and women, commonly older adults.

Leiomyoma of Kidney: It is a rare benign tumor of smooth muscle. A leiomyoma is seen among a wide range of adults and the kidney is an uncommon location for this tumor type.

Lipoma of Kidney: It is a benign tumor of fat cells (adipocytes). A lipoma is seen among a wide range of adults and can occur at various locations in the body. The kidney is an uncommon location for the tumor.

Lymphangioma of Kidney: It is a rare benign tumor of lymphatic blood vessels. A lymphangioma is seen among a wide age range of adults and can occur at various locations in the body. The kidney is an uncommon location for the tumor.

Lymphoma of Kidney: It is an uncommon lymphoma, which is generally observed in elderly men and women. The condition may be primary or secondary in nature.

MALT Lymphoma of Kidney: It is a rare non-gastric type of extranodal marginal zone lymphoma. It affects the kidney in older adults. The condition can be associated with autoimmune disorders.

MiT Family Translocation Renal Cell Carcinoma in Adults: A rare and aggressive type of renal cell carcinoma (kidney cancer) that develops from the renal cortex in adults. It is a malignant tumor that develops due to an abnormality within the tissue lining in the tubules of the kidney.

MiT Family Translocation Renal Cell Carcinoma in Children: A rare and aggressive type of renal cell carcinoma (kidney cancer) that develops from the renal cortex in children. It is a malignant tumor that develops due to an abnormality within the tissue lining in the tubules of the kidney.

Myelolipoma of Kidney: It is an extremely rare and benign tumor consisting of fat cells and hematopoietic cells, typically observed in adults. The kidney is an uncommon location for this tumor type.

Myxoma of Kidney: It is an extremely uncommon benign tumor of the kidney that is usually discovered incidentally. The tumor is seen in adults and may be present in the medulla or cortex of the kidney.

Oncocytosis of Kidney: It is a rare, benign condition of the kidney that is characterized by the presence of many oncocytic lesions/proliferations without necrosis in the kidney. It is generally diagnosed in adults.

Perineurioma of Kidney: It is a rare tumor of the perineurial cells, a type of cells that are present around a peripheral nerve sheath. Perineuriomas are generally benign in nature but may be occasionally malignant.

Primary Angiosarcoma of Kidney: It is a very rare, aggressive form of kidney cancer. The tumor is usually observed in middle-age and older adults

Primary Chondrosarcoma of Kidney: It is a rare and aggressive form of kidney cancer. The tumor is observed in both children and adults.

Primary Hemangiopericytoma of Kidney: It is a rare form of kidney cancer. The tumor is observed in teenagers and adults. It can arise from the renal capsule or perirenal tissue of the kidney.

Primary Liposarcoma of Kidney: It is an extremely rare and aggressive form of kidney cancer. The tumor may be observed in adults.

Primary Neuroblastoma of Kidney: It is a very rare and aggressive form of kidney cancer. It is considered to be a type of small blue cell tumor. The tumor is mostly seen in older children, teens, and young adults.

Primary Osteosarcoma of Kidney: It is a rare and aggressive form of kidney cancer. It is termed as an extraskeletal osteosarcoma. The tumor is observed in both children and adults.

Primary Rhabdomyosarcoma of Kidney: It is a very rare and aggressive form of kidney cancer. The tumor is observed in both children and adults.

Primary Synovial Sarcoma of Kidney: It is a rare, high-grade type of kidney cancer. The tumor is more commonly observed in individuals during adolescence and young adulthood.

Primary Thyroid-like Follicular Renal Cell Carcinoma: It is a rare histological variant of renal cell carcinoma (RCC) that mostly affects adult men and women. It is a low-malignancy potential tumor that rarely metastasizes.

Schwannoma of Kidney: It is a rare benign tumor that arise from the Schwann cells around the nerves; these tumors are essentially nerve sheath tumors. A schwannoma is often observed among a wide range of adults.

Simple Renal Cyst: It is a benign tumor indicating the presence of abnormal fluid-filled sacs in the kidney. It is typically seen among middle-aged and older adults.

Small Cell Carcinoma of Kidney: It is a rare and aggressive neuroendocrine type of renal carcinoma (kidney cancer). The malignant tumor affects adult males and females, generally older adults.

Spiradenocylindroma of Kidney: It is an extremely rare benign tumor of the kidney. Due to its rarity, the age and gender parameters are not well-known. The tumor is observed to be present in the cysts of the kidney.

Teratoma of Kidney: It is a very rare, usually benign tumor that arises from the pluripotent cells. It consists of a variety of tissue types including epithelial cells, bone, cartilage, nerve cells, and skin. This kidney tumor is mostly observed in children.

Transitional Cell Cancer of the Renal Pelvis and Ureter: It is a term used for transformation of normal cells to cancer cells in the renal pelvis and ureter. It is a rare condition that may affect individuals of all age groups.

Wilms’ Tumor: It is an infrequent, malignant solid tumor of uncertain derivation (unknown cell of origin). It affects the kidneys of very young children.