Although prostate cancer affects millions of men in the United States alone, one type of prostate cancer is the most common. Nearly all cases of prostate cancer are considered adenocarcinomas, with only an estimated 1-5 percent comprising all other types.1 While treatment options and presentation of prostate adenocarcinomas are frequently studied, less is known about the remaining types of prostate cancers. These additional, rare prostate cancers include prostate sarcomas, neuroendocrine tumors, small cell carcinomas, transitional cell carcinomas, and squamous cell carcinomas. Because they are so rare, there is still more research to be done on their characteristics and treatment options.
Most common type of prostate cancer
As mentioned, adenocarcinomas make up the vast majority of prostate cancer cases. It has been estimated that roughly 95-99 percent of all prostate cancers fall into this category. Within this classification, roughly 9 out of 10 adenocarcinomas are acinar, while the small remaining fraction is ductal. Acinar adenocarcinomas develop in acini cells and increase PSA (prostate-specific antigen) levels. These cells form clusters and line fluid secreting glands. In the prostate, acini line the gland and produce the fluid that will eventually become semen. Ductal adenocarcinoma, on the other hand starts in the cells that line the tubes and ducts of the prostate gland, and doesn’t always impact PSA levels, making it potentially harder to detect. In addition, ductal adenocarcinomas often spread faster than acinar adenocarcinomas.1-4
Soft tissue prostate cancer
Sarcomas comprise less than 0.1 percent of all primary prostate cancer cases, and develops in soft tissues. Soft tissue includes muscles and nerves. Although bones connect and support bodily structures, they are not considered soft tissue. Since soft tissue can be found all over the body, these cancers can develop and spread to just about anywhere. Although sarcomas can grow in the lymphatic vessels, blood vessels, and smooth muscles of the prostate, the most common place to find these once they break away and spread is in the lungs. The two most common prostate sarcomas include leiomyosarcomas and rhabdomyosarcomas, which can affect younger men between ages 35 and 60, however, extremely rare cases have been found in children. Prostate sarcomas are hard to detect and usually do not change PSA levels.3,5,6
Neuroendocrine Tumors (NETs)
Neuroendocrine tumors are also referred to as carcinoids. These tumors are present in the neuroendocrine system, which is comprised of the nerve and gland cells responsible for making and releasing hormones into the bloodstream. These tumors often grow slowly and most often start in the digestive system (GI tract), before moving other places, such as the prostate. NETs are extremely rare, so not as much information is known about their origin and development. However, it has been discovered that NETs do not affect PSA levels and that they seem to be hereditary in nature. These tumors can begin to secrete their own hormones that lead to symptoms such as diarrhea, wheezing, fast heart beat, dizziness, and flushing of the skin. These symptoms together, as a result of a hormone-secreting NET, is referred to as carcinoid syndrome.7
An aggressive type of prostate cancer
Prostate small cell carcinoma is another type of neuroendocrine cancer, however, they are made from small round cells and are more common than NETs. Small cell carcinoma is very aggressive and also does not induce a change in PSA levels. They comprise less than 1 percent of all prostate cancer cases and once they are finally discovered, the cancer has often already metastasized and is well beyond early treatment options like hormone therapy. The prognosis for small cell carcinoma is very poor, often presenting with an estimated life expectancy of less than a year.2,3,6
Cancer starting outside the prostate
Transitional cell carcinoma, also known as urothelial cancer, typically starts in the structures surrounding the prostate, including the cells lining the urethra (the tube the carries urine out of the body from the bladder), or the bladder. Prostate cancer can develop as the primary tumors in the urethra and bladder break off and start locally spreading. Although it is incredibly rare, it is possible for this type of cancer to begin in the prostate and then spread to the bladder, however, this carcinoma typically presents the other way around. Transitional cell carcinoma often presents with blood in the urine or difficulty urinating. Advanced treatment options may be necessary when battling this type of cancer depending on how far it has spread.2,3,6
Rare, fast-growing cases
Squamous cell carcinoma is another incredibly rare and fast-growing type of prostate cancer. This type of prostate cancer does not start in the gland cells, like adenocarcinoma, but rather, starts in the flat cells that cover the prostate gland itself. Squamous cell carcinoma is very aggressive.2,6
This is not an exhaustive list of all potential types of prostate cancers nor all of their characteristics. As mentioned earlier, since non-adenocarcinomas are incredibly rare, the scientific community is constantly working to gain more information on these categories.