There are a number of rarer types of prostate carcinoma that sometimes occur; they are notable for not having a Gleason Score and are often more aggressive than the more common acinar adenocarcinoma.
Ductal adenocarcinoma is a rare (1%) type of prostate cancer. It may arise alone or in combination with the more usual acinar type. They are notable for normal or only slightly raised serum PSA levels. The pure form is often located centrally and may be diagnosed during a TURP for obstructive symptoms.
On microscopy, ductal adenocarcinoma is notable for a pseudostratified columnar epithelium (in contrast to the simple cuboidal/columnar epithelium of the acinar type). Immunohistochemistry stains are positive for PSA (despite low serum levels).
Ductal adenocarcinoma is usually more aggressive than acinar adenocarcinoma; metastases are more frequent and there is less uniform response to androgen deprivation.
Urothelial or transitional cell carcinoma is thought to arise from the urothelium lining the prostatic urethra and adjacent prostatic ducts. It accounts for about 1-2% of primary prostate cancers. It presents with obstructive symptoms and is usually an incidental finding on TURP.
These tumours stain negatively for PSA which can be used to differentiate them from poorly differentiated prostate cancers in some circumstances.
Prognosis is poor if the tumour is invasive but very good for in situ disease. For a full discussion of urothelial carcinoma see the Urinary Tract Pathology topic.
Neuroendocrine tumours may present as areas of focal differentiation within an acinar adenocarcinoma; as carcinoid tumours; or as small cell tumours of the prostate.
- Although areas of neuroendocrine differentiation are seen in most adenocarcinomas, the term 'focal differentiation in prostatic adenocarcinoma' refers to zones with large clusters of neuroendocrine cells within the tumour. The prognostic significance is unclear at this stage.
- Carcinoid tumours are very rare and evidence regarding their prognosis and treatment is scanty
- Small cell carcinoma of the prostate is an uncommon disease that may arise from an acinar adenocarcinoma or de novo. It resembles small cell carcinoma of the lung. Prognosis is terrible with a very low 1 year survival. Response to hormonal manipulation is thought to be poor but low numbers of cases limits the available evidence.
Squamous cell carcinoma of the prostate is very rare and aggressive disease that frequently metastasises. There are less than 100 cases reported worldwide.
Basal cell carcinoma is very rare. It may resemble BCC of the skin or take on a number of other patterns. It has been known to metastasise.