Acinar adenocarcinoma is by far the most common type, with five stages of differentiation graded by the Gleason Score. Grade 1 regions are well differentiated with gland formation, whereas grade 5 regions demonstrate no normal structure and have a high nuclear grade. The tumorus are typically difficult to visualise on macroscopic examination.
Ductal carcinoma is uncommon and arises from the ducts linking the acini with the urethra.
Small cell carcinoma is a rare type of prostatic tumour, with characteristic neuroendocrine features (nests/pallisading/trabeculae, positive immunohistochemistry for neuroendocrine markers).
Metaplasia into squamous carcinoma is rare.
Prostatic intraepithelial neoplasia
Prostatic intraepithelial neoplasia (PIN) is an incidental finding on prostate biopsy and resection. Unlike invasive carcinoma, it retains the myoepithelial layer and basement membrane. Its significance is unknown, although it is thought to be a precursor much like DCIS for breast cancer.
Sarcoma and primary haemotological tumours of the prostate are very rare.
Natural History and Patterns of Spread
Acinar adenocarcinoma typically grows more slowly than other types of cancer. It frequently invovles the entire gland but may be localised. Obstructive symptoms present at a late stage as the tumour typically arises in the peripheral parts of the gland, distant from the urethra. Local invasion may lead to penetration of the prostate capsule or invasion of the seminal glands, which convey a worse prognosis. The bladder or rectum may also be invaded in later stage disease.
Prostate cancer may spread to regional lymph nodes, typically in the internal iliac chain. The presacral and external iliac nodes are rarely involved.
Haemotogenous spread occurs classically to bone, but the liver may also be involved. It confers incurability and a poorer prognosis.
Ductal carcinoma may arise in the central ducts, leading to obstructive symptoms and haematuria. It has a poorer prognosis.
Small cell carcinoma has a very poor prognosis, metastasises early and is usually incurable.
Prostate Intraepithelial Neoplasia
The potential of PIN to develop into invasive carcinoma is not known, as it is nearly always an incidental finding on prostate microscopy. It seems to occur in similar regions to acinar adenocarcinoma.
Sarcomas typically invade locally and metastasise haemotogenously.