Kidney Cancer: Causes and Types
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Kidneys are bean shaped organs located on the posterior side of the abdomen one on each side of the vertebral column. The left kidney lies a little higher than the right one. Each kidney is enclosed with a transparent membrane called renal capsule and is divided into outer renal cortex and inner renal medulla. The capsule protects the kidneys against infections and trauma. The renal cortex is convex in shape whereas the renal medulla is concave. The outer cortex is surrounded by a tough fibrous capsule. A capsule called renal pelvis is attached on the indented side of the kidney. This capsule extends into the ureter. The primary function of the kidney is to regulate the electrolytes and maintain the acid-base balance of the body to create a stable environment for tissue and cell metabolism. The other important functions are excreting metabolic waste products, conserving nutrients and water transport.
The medulla is made up of pyramidal structures known as renal pyramids. The apex of the pyramid is known as papilla and meets the calyx, which is a branch of the renal pelvis. The basal portion of the pyramid is elongated and grows towards the cortex and the space between the renal pyramids is known as renal columns.
The cortex of kidney is made up of two types of tissues
Labyrinth of Ludwig or cortical substance proper
The medulary rays are also known as 'Henle', which are cylindrical in shape and are aligned parallel to each other. The medullary rays are the extensions of the pyramidal structures and the cortical substance proper is interspaced between them. The 'labrynth of Ludwig' contains small structures known as glomeruli or Malphigian tubules.
Renal pelvis or artery
The renal artery enters the concave side of the kidney through the hilum and branches out in the cortical portion. The artery branches out in right angles and these branches at the base of renal pelvis are known as major calyx and the others, which are away from the renal pelvis, are smaller in size known as minor calyx.
The region between the main parts of the kidney is made up blood vessels, stroma and colleting tubules. These regions of the kidney appear like colloidal substance altogether.
These are small tubes, which are either straight or twisted. The tubules originate from sac-like structure present around the glomerulus known as the Bowman's capsule. The walls of the tubules are lined with epithelial cells, which are striated due to the presence of cylindrical objects called rods of Heiderihain.
These are the important units of kidney, which filter the blood to control and regulate the concentration of the substances, like water and salts of sodium. The renal tubules in the nephrons excrete waste materials, while the renal corpuscles reabsorb the necessary substances. These nephrons regulate blood pressure and blood volume. Two types of nephrons are present
Kidney cancers caused due to smoking
The most common type of kidney cancer is renal cell carcinoma which account for about 90% of the total kidney cancers. Here malignant cells arises from the tubules of the kidney.
The following are also types of kidney cancers:
- Squamous cell carcinoma
- Clear-cell sarcoma of the kidney
- Mixed epithelial stromal tumour
- Smoking mainly causes two types of cancer in kidney
- Renal Cell Carcinoma
- Transitional Cell Carcinoma
- Renal cell carcinoma
Smoking increases the risk of developing kidney cancer as the harmful chemicals in cigarettes are absorbed into the blood stream and the blood is filtered in the kidneys. Many of these chemicals are trapped and some of them cause damage to the cells and later becomes cancerous causing renal cell carcinoma. The cells usually affected are the tubular epithelial cells in the renal cortex region. These tumours are either cystic or solid and spread to other organs like the adrenal glands, spleen, colon and pancreas.
Stages of Renal Cell Carcinoma
There are four stages in Renal Cell Carcinoma
- Stage I
In this stage, the tumour is about 7 cm in size and is confined to the Kidneys.
- Stage II
In this stage, the cancer spreads to the fat tissue around the kidney and the size is larger than 7cm.
- Stage III
There are three possible situations in this stage:
- The cancer is confined to the kidney, but the cancerous cells enter the lymph system and also invade into the adjacent lymph node.
- The cancer spreads to the adrenal gland, fat tissue and fibrous tissue, which are found in the kidney. The tumour may also be present in one of the lymph nodes
- The cancer spreads to the renal vein that carries clean blood from the kidneys or to the main blood vessel, which carries blood from the lower parts of the body to the heart.
- Stage IV
This stage, there are three possible situations
- The cancer spreads beyond the fibrous tissue that surrounds the kidney
- Cancerous cells are found in several lymph nodes
- The cancer spreads to adjacent organs like bowel, pancreas or lungs.
Clear Renal cell carcinoma
It is the most common type of renal cell carcinoma caused due to smoking. The cancer cells originate from the mature renal tubular cells in the proximal tubule of the nephron. This type of cancer is caused due to the deletion or translocation of the short arm of chromosome 3. The cancer is confined only to the organ hence it is easy to treat this type of cancer.
Transitional cell carcinoma
The cancer cells originate from the "transitional cells" that lines the pelvis region of Kidneys and Ureters. The cancer cells differ from those of the renal cell carcinoma. The cancer cells spread through two ways:
By epithelial cells that line the organs and many passageways that exit the body
Through lymphatic system
Stages of Transitional Cell Carcinoma
There are five stages in the development of transitional cell carcinoma
- Stage 0 (papillary carcinoma and carcinoma in Situ)
The abnormal cells are found in the tissue lining of the renal pelvis and these cells become cancerous and spread to the nearby normal tissue. This stage is divided into two depending on the type of tumour formed
Stage 0a - the tumours look like tiny mushrooms growing from the lining. It is also called non-invasive papillary carcinoma.
Stage 0is - it is a flat tumour on the tissue lining of the renal pelvis and is called carcinoma in situ.
- Stage I
In this stage, the cancer spreads through the lining of the renal pelvis into the layer of connective tissues.
- Stage II
In this stage, the cancer spreads from the layer of connective tissue to the muscle layer of the renal pelvis.
- Stage III
The cancer spreads to the layer of fat outside the renal pelvis or into the wall of the kidney.
- Stage IV
The cancer spreads to either
- Nearby organ
- Fat layer of Kidney
- One or more lymph nodes
Risk factors for transitional cell carcinoma
- Understanding at genetic level
- Genetic alterations at 5q22.2-q23.1, where the LOX gene is located,
- RASSF1A 3p21.3 deletion polymorphism
- VHL gene mutation 3 mutation are involved (3 G:C-A:T and 1A:T-G:C)-somatic and LOH 3p25.5.
- Promoter hypermethylation in RCC has also been observed for the NORE1A, TIMP3, DAPK, and MT1G genes
- FLCN gene mutation causes brdge-hogg dube syndrome-m-TOR PATHWAY.
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