by Trevor A. Flood, MD FRCPC
May 11, 2022
Chromophobe renal cell carcinoma is a type of kidney cancer. The tumour develops from the very small tubules in the kidney. Chromophobe renal cell carcinoma is the third most common type of kidney cancer in adults. These tumours generally have an excellent prognosis except when sarcomatoid or rhabdoid cells are found.
Most cases of chromophobe renal cell carcinoma are sporadic which means they occur by chance and are unrelated to any known genetic condition. Some patients, however, are born with a syndrome, a genetic condition, that makes them more likely to develop multiple chromophobe renal cell carcinomas and to develop them at a younger age.
One genetic syndrome that is associated with the development of chromophobe renal cell carcinoma is called Birt Hogg Dubé syndrome. Birt Hogg Dubé syndrome is characterized by the growth of multiple kidney tumours, including chromophobe renal cell carcinoma. Other features of this syndrome include benign (non-cancerous) skin tumours and cysts in the liver.
Many chromophobe renal cell carcinomas are found incidentally at the time of abdominal imaging for other reasons. Patients with these tumours may occasionally experience pain in their back or side or notice blood in their urine. The tumour will appear as a kidney mass on MRI or CT scan of the abdomen.
The diagnosis of chromophobe renal cell carcinoma can be made after a small sample of tissue is removed in a procedure called a biopsy. Depending on the results of the imaging studies, your doctor may suggest removing the tumour without first performing a biopsy.
When examined under the microscope, the tumour cells in chromophobe renal cell carcinoma are polygonal in shape and the cells connect together to form large groups called sheets. The cells appear light pink to clear. Tumours with these kinds of cells are less likely to spread to other parts of the body and are associated with an excellent prognosis.
The microscopic appearance of chromophobe renal cell carcinoma.
Sometimes, more than one tumour is found in the same kidney. When only one tumour is found, pathologists call this unifocal. When more than one tumour is found, pathologists call this multifocal.
When multiple tumours are found, they are usually of the same type. For example, they are all chromophobe renal cell carcinomas. However, different types of tumours can also be found in the same kidney. In that case, your report will list and describe each type of tumour found.
Pathologists divide chromophobe renal cell carcinoma into two grades – low and high – based on how much the tumour cells look like the cells normally found in the kidney. The grade can only be determined after the tumour has been examined under the microscope.
Chromophobe renal cell carcinomas tend to look and behave similarly. They are associated with an excellent prognosis (except when sarcomatoid or rhabdoid cells are present or when they present at a high pathologic tumour stage; see sections below). For this reason, most tumours are considered low grade.
Sarcomatoid cells are tumour cells that have changed both their shape and their behaviour. Sarcomatoid tumour cells can be found in almost all types of renal cell carcinoma, including chromophobe renal cell carcinoma. Instead of being polygonal in shape, the sarcomatoid cells are now long and thin. Pathologists describe cells with this shape as spindle cells. Tumours with sarcomatoid cells are associated with a worse prognosis because they are more likely to spread to other parts of the body.
Rhabdoid cells are tumour cells that have changed to look more like muscle cells. Rhabdoid tumour cells can be found in almost all types of renal cell carcinoma, including chromophobe renal cell carcinoma. Like sarcomatoid cells, tumours with rhabdoid cells are associated with a worse prognosis.
Necrosis is a form of cell death and it commonly occurs in cancerous tumours. Your pathologist will closely examine the tumour for evidence of necrosis. The presence of necrosis is important because it is associated with a worse prognosis.
The normal kidney sits near the back of the body and is surrounded by fat. The adrenal gland sits directly above the kidney and the bladder is attached to the kidney by a long thin tube called the ureter which connects to the kidney in a region called the ‘renal sinus’. Chromophobe renal cell carcinoma starts inside the kidney but as it grows, it can extend into any of these structures and organs. The growth of the tumour into surrounding organs is called tumour extension.
Your pathologist will carefully examine the specimen for any evidence of tumour extension and all structures or organs involved will be listed in your report. Tumour extension into any of these structures or organs is important because it is associated with a worse prognosis and it is also used to determine the pathologic stage (see Pathologic stage below).
A margin is the normal tissue that surrounds a tumour and is removed with the tumour at the time of surgery. If only part of the kidney was removed (a procedure known as a ‘partial nephrectomy’), the margins will include the fat surrounding that portion of the kidney and the area where the kidney was divided.
If the entire kidney was removed (a procedure known as a ‘total’ or ‘radical nephrectomy’) the margins will include the fat surrounding the kidney, the ureter (the tube that connects the kidney to the bladder), and some large blood vessels (usually arteries and veins). Some larger specimens may include additional margins.
A margin is considered positive when the cancer cells are seen at the cut edge of the tissue. Your pathologist will report any positive margins and the location of that margin. A positive margin is associated with an increased risk of the tumour coming back in the same area of the body.
Blood moves around the body through long thin tubes called blood vessels. Another type of fluid called lymph which contains waste and immune cells moves around the body through lymphatic channels. The term lymphovascular invasion is used to describe tumour cells that are found inside a blood vessel or lymphatic channel. Lymphovascular invasion is important because once the tumour cells are inside a blood vessel or lymphatic channel they are able to metastasize (spread) to other parts of the body such as lymph nodes or the lungs.
Lymph nodes are small immune organs located throughout the body. Tumour cells can spread from the tumour to a lymph node through lymphatic channels located in and around the tumour (see Lymphovascular invasion above). The movement of tumour cells from the tumour to a lymph node is called lymph node metastasis.
Your pathologist will carefully examine each lymph node for tumour cells. Lymph nodes that contain tumour cells are often called positive while those that do not contain any tumour cells are called negative. Most reports include the total number of lymph nodes examined and the number, if any, that contain tumour cells.
The pathologic stage for chromophobe renal cell carcinoma is based on the TNM staging system, an internationally recognized system originally created by the American Joint Committee on Cancer. This system uses information about the primary tumour (T), lymph nodes (N), and distant metastatic disease (M) to determine the complete pathologic stage (pTNM). Your pathologist will examine the tissue submitted and give each part a number. In general, a higher number means more advanced disease and a worse prognosis.
Chromophobe renal cell carcinoma is given a tumour stage between 1 and 4 based on the size of the tumour and the growth of the tumour into organs attached to the kidney.
Chromophobe renal cell carcinoma is given a nodal stage of 0 or 1 based on the presence of tumour cells in a lymph node. If no lymph nodes are involved the nodal stage is 0. If any tumour cells are seen in a lymph node the nodal stage is 1. If no lymph nodes are sent for pathological examination, the nodal stage cannot be determined and the nodal stage is listed as NX.
Chromophobe renal cell carcinoma is given a metastatic stage of 0 or 1 based on the presence of tumour cells at a distant site in the body (for example the lungs). The metastatic stage can only be determined if tissue from a distant site is sent for pathological examination. Because this tissue is rarely present, the metastatic stage cannot be determined and is listed as MX.
The non-neoplastic kidney is the tissue outside of the tumour. Your pathologist will carefully examine the non-neoplastic tissue for evidence of other diseases that can commonly affect the kidney such as arterionephrosclerosis (high blood pressure) and diabetic nephropathy (diabetes).