Treating manly woes
The prostate gland is an important part of a man but is frequently neglected.
THE prostate gland, though a small organ weighing approximately 20g, is an important part of the male reproductive system.
The prostatic fluid which it produces nourishes and protects the sperms after they have been deposited in the female vagina during sexual intercourse. The muscles of the prostate gland also play a role during the ejaculation of semen.
The prostate gland is frequently neglected until men develop problems such as urinary obstruction or hematuria (blood in the urine). In most men, the prostate gland continues to grow in size with age, leading to benign prostatic hyperplasia. In some men, the prostate gland can become cancerous.
In the United States, prostate cancer is the most common cancer among men and the second leading cause of death. In Malaysia, prostate cancer has been reported to be the fifth most common cancer affecting men.
Though it is a relatively slow-growing cancer, there are prostate cancer subtypes that need to be dealt with immediately and appropriately.
An enlarged prostate gland may cause urinary urgency and hesitancy, straining to urinate, weak urinary stream, incomplete urinary voiding, urinary dribbling, urinary frequency and nocturia (frequent urination at night).
The clinician whose specialty is in managing such cases – urologist, will do the necessary examinations including per rectal examination of the prostate glands, measurement of prostate specific antigen (PSA) and prostate biopsy if indicated.
Once confirmed to be prostatic cancer, the urologist will stage the disease for prognostication and to determine the treatment. The current standard treatments for prostate cancers include active surveillance, watchful waiting, radical prostatectomy, radiation therapy, hormonal therapy and radioactive therapy.
According to the US data, 78.2% are diagnosed at the local stage and men with localised prostate cancer have a five-year relative survival of nearly 100%. Even for patients with regional disease, which can be detected on magnetic resonance imaging (MRI), they have similar five-year relative survival with proper treatment.
On the contrary, the five-year relative survival for distant metas- tasis drops significantly to 30%.
The most frequent sites for metastases in prostate cancer are the bone (90%), lung (46%) and liver (25%). Assessment of the skeletal system for bone metastases is routinely performed for patients with intermediate to high risk.
Whenever available, the goal standard of skeletal assessment would be using bone scintigraphy either using Technetium-99m methylene disphosphonate (99m Tc-MDP) or Fluorine-18 sodium fluoride (18F-NaF) scan.
These nuclear medicine-based scans are very sensitive and are approximately 10 times more sensitive compared to conventional radiographic imaging.
Early detection of bone metastases is definitely advantageous as appropriate therapies can be administered accordingly and prevents further progression of the disease. Bone scintigraphy is also useful in monitoring of metastatic prostate cancer to determine the clinical benefit to systemic therapy or even bone palliation.
Though bone scintigraphy utilises radioactives, the radiation exposure to patients is rather low with effective dose of approximately 6.3 millisieverts in an adult undergoing a whole body 99m Tc-MDP scan.
Bone scintigraphy is currently available locally in most government and university-based hospitals, and in a number of private nuclear medicine centres. However many prostate cancer patients with bone metastases are still not being referred for bone scintigraphy due to logistic and financial constraints as well as lack of awareness on the availability of such services in the country.
Local external beam radiation (EBRT) may be performed in patients with localised bone metastasis but in patients with extensive bone metastases resistant to castration, EBRT is not possible.
Fortunately, bisphosphonate such as zolendronic acid, and human monoclonal antibodies such as denosumab has proven to be useful in management of bone metastases.
Bone metastases can be painful and frequently debilitating, especially when it is extensive. The use of analgesics is frequently insufficient and long-term use may lead to further complications such as gastric ulcers and constipation. Since the five-year survival of such patients is poor, improving the quality of life is important. Bone palliation using various radioactives such as Radium-223, Samarium-153 and Strontium-89 has been shown to provide pain relief, decrease analgesic consumption and improve overall survival.
The use of 68Gallium- prostate-specific membrane antigen (68Ga-PSMA) PET/CT in prostate cancer has been extensively studied over the years and is now available in most countries including Malaysia. The 68Ga-PSMA is a very sensitive imaging tool and has been shown to be able to detect lesions that may not have been apparent on MRI.
It is indeed a must-have armament for urologists dealing with prostate cancer patients with elevated PSA levels but no evidence of disease on conventional imaging.
In addition to detection of the metastatic sites, 68Ga-PSMA provides the clinician with another treatment option – the use of 177Lutetium-PSMA (177Lu-PSMA) therapy for metastatic castrate-resistant prostate cancer (mCRPC).
A positive scan (metastases detected) on 68Ga-PSMA means 177Lu-PSMA can be used for therapy. Studies have shown very good outcomes for patients with mCRPC using this therapy.
Nevertheless, 177Lu-PSMA is not a magic bullet as not all prostate cancers will respond to this treat- ment nor will all prostate cancer be detected by 68Ga-PSMA.
The role of nuclear medicine in the management of prostate cancer is rapidly expanding. Molecular imaging and therapy is the future of medicine. Notwithstanding, urologists as the gatekeepers, will assist prostate cancer patients in selecting the best treatment. Internet-derived information is useful but do not let it obstruct treatment which is tailored for each individual.
In short, the prostate gland may just be another small organ in the body but it is an important part of the male anatomy. Pick a bone with prostate cancer and get medical attention early.
Dr Alex Khoo Cheen Hoe is a consultant nuclear medicine physician based in Penang.