What Is Kidney Cancer

Executive Summary

The primary function of the kidney is to remove impurities, water, salts, and minerals from blood in the urine. There are two kidneys in every individual, and each of them functions independently. Each kidney is also attached to a tube-like structure, the ureter. It also carries the waste product from the kidneys called urine to the urinary bladder. Cancer in the kidneys begins when normal, healthy cells in one or both kidneys undergo mutation and proliferate without control, leading to a mass called a renal cortical tumor. Several types of kidney cancer also involve renal cell carcinoma, urothelial carcinoma, sarcomas, wilms tumor, and lymphoma. Pathologists have also identified around 30 different types of kidney cancer cells. Some of the most common types of kidney cancer cells include clear cell, papillary, sarcomatoid features, medullary, collecting duct, chromophobe, oncocytoma, and angiomyolipoma.

About the kidneys

Every person has a pair of kidneys, and they are located in the abdomen, precisely above the waist region, on both sides of the spine. Each kidney is about 10 to 12 centimeters long, 3 to 5 centimeters thick and 5 to 7 centimeters wide.

The primary function of the kidney is to remove impurities, water, salts, and minerals from blood in the urine. They are the filtering unit of the body. It also helps retain essential chemicals like potassium, calcium, and sodium in the body balanced. These organs play a vital role in controlling and maintaining the body’s fluid balance. The kidneys also generate hormones that help control blood pressure, stimulate the bone marrow to create red blood cells, and aids in other body functions.

Every day the kidneys filter around 200 quarts of blood to produce 2 quarts of urine. The ureter carries the waste product from the kidneys called urine to the urinary bladder. Most people have two kidneys, and each of them functions independently and this also indicates that the body can properly function even with a single functioning kidney. Also at present, with a filtering process called dialysis, it is possible to even live without a fully functioning kidney. When performed through the blood, dialysis is called haemodialysis.

About kidney cancer

Cancer in the kidneys begins when normal, healthy cells in one or both kidneys undergo mutation and proliferate without control, leading to a mass called a renal cortical tumor ^​1​. A tumor is a mass that can be benign, malignant or indolent additionally, an indolent tumor is a cancerous growth that rarely spreads or metastasize to other body parts. Also a malignant tumor refers to an aggressive tumor that grows and spread rapidly to other parts of the body. A benign tumor is a tumor that grows but does not spread or metastasize to other body parts.

Types of kidney cancer

Renal cell carcinoma

Renal cell carcinoma is the most common type of adult kidney cancer type. Around 85% of kidney cancers diagnosed are renal cell carcinoma. This type of kidney cancer originates in the proximal renal tubules that make up the kidney’s filtration system ^​2​. There are thousands of such tiny filtration units in each kidney. 

Urothelial carcinoma

Urothelial carcinoma is also transitional cell carcinoma. It accounts for 5% to 10% of adult kidney cancers. This type of carcinoma starts in the kidney, where urine gets collected and moves to the urinary bladder. This type of kidney cancer is treated just like bladder cancer since both types of cancer begin in the same cells that line the bladder and renal pelvis ^​3​.

Sarcoma

Sarcomas of the kidney are rare. The type of cancer begins in the soft tissue of the kidney, or the thin layer of connective tissue surrounding the kidney, called the capsule, or in the surrounding fat. These cancerous growths commonly recur in the kidney area or metastasize to other body parts. Medicated therapies like chemotherapy and additional surgeries may be prescribed after the initial surgical procedures.

Wilms tumor

The type of tumor is most common in children. The treatment strategy for Wilms tumor is different from adult kidney cancer cases. The type of tumor accounts for about 1% of all kidney cancer cases diagnosed. Wilms tumor is more likely to be successfully treated with chemotherapy, radiation and surgery than any other kind of kidney cancer ^​4​. 

Lymphoma

Lymphoma cause enlargement of both kidneys. The cancer condition is associated with enlarged lymph nodes. The condition can cause enlargement of lymph nodes in the chest, neck, and abdominal cavity. In some rare cases, a kidney lymphoma can appear as a lone tumor mass in the kidney, including some enlarged regional lymph nodes. If a lymphoma is suspected, the doctor may perform a biopsy to confirm the diagnosis. They might also recommend surgery and chemotherapy as treatment procedures.

Types of kidney cancer cells

Understanding the type of cells that makes up tumor growth in the kidney can aid doctors to diagnose the disease condition accurately and proceeding with the most effective treatment strategy. Pathologists have identified around 30 different types of kidney cancer cells. (a pathologist is a doctor who specializes in analyzing the test samples and examining the cells, tissues, and organs to diagnose the disease condition.). Sometimes imaging tests like magnetic resonance imaging (MRI) or Computed tomography (CT) scans may not distinguish between malignant, indolent, benign, or malignant renal tumors before surgical procedure.

The following are the most common types of kidney cancer cells. A tumor grade refers to the degree of differentiation of cells and not how rapidly the cells are growing. Differentiation indicates how much the tumor cells look like healthy normal cells. If the grade of a tumor is high, it is more likely that the tumor may metastasize to other body parts over time.

Clear cell

70% of all cases of kidney cancers are clear cells. Clear cells range from slow-growing or grade 1 to fast-growing or grade 4. Targeted therapy and immunotherapy are effective in treating clear cell kidney cancer.

Papillary

About 10% to 15% of kidney cancer is Papillary kidney cancer. There are two types of kidney cancer, type 1 and type 2. Localized papillary kidney cancer is treated with surgery. If papillary kidney cancer metastasizes, it is also treated with blocking agents. Many researchers are still studying the effectiveness of immunotherapy in treating metastatic papillary cancers ^​5​. Doctors also recommend different clinical trials for patients with metastatic papillary cancers.

Sarcomatoid features

All these kidneys mentioned above cancer cell sub-types like 

Clear cell, chromophobe, papillary, etc., can show highly disorganized features when viewed under a microscope. Pathologists often describe these tumor cells as sarcomatoid. Sarcomatoid is not a distinct tumor subtype, but when these features are seen, doctors are aware that this is a very aggressive type of kidney cancer. Many promising scientific research studies (like new immunotherapy options) treat people with tumors possessing sarcomatoid features. Most recent progress in terms of treatment includes combinations of nivolumab (Opdivo) and ipilimumab (Yervoy) as well as combinations of bevacizumab (Avastin) and atezolizumab (Tecentriq).

Medullary

This is a rare but highly aggressive cancer but still a renal cortical tumor. Additionally, sickle cell trait means that the person has inherited the sickle cell gene and based on some scientific data, the currently recommended treatment options include combinations of chemotherapy with blood vessel inhibitors. Also, many clinical trials are going on to devise better treatment options.

Collecting duct

Collecting duct kidney cancer is also more likely to occur in people between 20 and 30 years. It starts in the collecting ducts of the kidney and hence, collecting duct carcinoma is closely related to transitional cell carcinoma. This cancer condition is also challenging to treat successfully for the long term, even with combinations of systemic medicated therapies like chemotherapy and surgery.

Chromophobe

This is another uncommon cancer that may form indolent tumor growths that are unlikely to metastasize but can be aggressive if they spread. Clinical trials are also underway to discover the best ways to treat this cancer type.

Oncocytoma

Oncocytoma is also a kidney cancer type that grows at a slow pace and the chance of this tumour spreading is infrequent. Surgery is the preferred method to treat this type of cancer.

Angiomyolipoma

Angiomyolipoma is a benign tumor type that has a unique appearance when viewed under a microscope and on a CT scan. The tumor is also less likely to grow and metastasize. The form of cancer is usually treated with surgery. Significant bleeding is not common but can be expected in the case of pregnant and premenopausal women. Epithelioid is an aggressive form of angiomyolipoma, which in rare instances can invade the inferior vena cava and the renal vein and metastasize and affect the nearby lymph nodes or organs, such as the liver.

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