Different types of kidney tumours grow at different rates, have different prognoses and react differently to treatment. Determining the type of tumour is called histopathology.
BHD-related kidney cancer can be chromophobe, papillary or clear cell renal cell carcinoma (RCC). There have also been reports of mixed types as well as less common types. In the largest study to date of BHD-associated tumours, most were either solely benign oncocytomas or oncocytomas mixed with a type of cancerous kidney tumour. While among these types, chromophobe RCC is considered to have the best prognosis, followed by papillary and then clear cell RCC, recent studies have shown that the type of RCC is actually not as important as other variables, such as the stage and grade of the tumour. Therefore, it is important to be monitored regularly so that any potential cancer can be detected early.
Chromophobe kidney cancer is considered less aggressive than other forms of RCC, and is not usually metastatic in individuals affected by BHD, although metastatic cases have been reported. About 23% of BHD-related kidney tumours are chromophobe.
Although papillary renal cell carcinoma has been identified in BHD syndrome, it is not common. Papillary renal cell carcinoma (especially Type 2) can be aggressive and result in metastasis.
- Clear cell
Clear cell is one of the most common types of renal cell carcinoma. It is not generally considered common in families with BHD syndrome, though some doctors have recently identified more cases than expected. Clear cell carcinoma has also been identified in some hybrid tumours.
Oncocytomas are considered to be benign kidney tumours. While benign, oncocytomas can damage the kidneys as they may grow in places that might affect kidney blood flow or kidney function.
This type of tumour does not metastasise, or spread, to other parts of the body. About 3% of BHD-related kidney tumours were classified as oncocytic in the largest study of BHD kidney tumours to date.
- Hybrid tumours
Hybrid tumours are a mixture of two types. Several hybrids have been reported in BHD-related tumours, including oncocytic and chromophobe, and clear cell and chromophobe. In a study of 34 individuals with BHD-related kidney tumours, 67% of the tumours were identified as hybrid oncocytic/chromophobe.
- Other tumours
There have also been reports of other types of benign kidney tumours in BHD patients, such as renal angiomyolipomas, which are typically associated with tuberous sclerosis complex.
Kidney cancer classification
If/when your kidney cancer is examined by a pathologist, you will be told its stage, grade and state.
There are four stages, labelled I, II, III, and IV.
- In stages I and II, the cancer is confined to the kidney; it has not spread to other organs or lymph nodes. Most BHD-related tumours are Stage I or II. Stage I tumours are smaller than 7 centimetres (2.75 inches), while Stage II tumours are larger.
- Stages III and IV are used to designate cases where the cancer has metastasised (spread). Stage III cancers have spread to lymph nodes, local veins or the fat surrounding the kidney; Stage IV cancers have spread to distant organs and tissues. Metastasis is rare in BHD syndrome.
Grades are assigned a number from 1-4 and correspond to the appearance, aggressiveness and growth rate of the cancer. Grade 1 tumours appear more similar to normal cells and are the slowest-growing, while Grade 4 cancers are the most abnormal and aggressive. A lower grade usually corresponds to a better prognosis. Research seems to indicate that BHD-associated renal tumours are slow growing.
You may also come across the TNM system, which divides stages and grades in more detail. For more information on how the TNM system works, visit Macmillan’s article on Staging and grading of kidney cancer.
There is also the classification of primary vs. metastatic state.
- Primary tumours have grown from their cell of origin.
- Metastatic tumours originate from cancerous cells which have travelled to another part of the body.
The prognosis for BHD-related kidney cancer is, on the whole, positive. BHD-related cancers do not normally metastasise and so offer a good target for effective treatment.
Publication date: September 2012
Review date: September 2015