Prostate Cancer

Overview

By Tina Shahian, PhD

Prostate cancer is cancer of the cells of the prostate, which is a small walnut-shaped gland below the urinary tract and in front of the rectum. The prostate organ is part of the male reproductive system, and is responsible for producing some of the fluid that nourishes and helps transport sperm. Prostate cancer is not to be confused with benign prostate hyperplasia (BPH) or “enlarged prostate”. BPH is an age-related growth of the prostate that is unrelated to cancer.  

prostate highlighted beneath urinary bladder (lateral view)Prostate cancer is the second most common cancer in men in the United States, with an estimated one out of seven men becoming diagnosed. The great majority of prostate cancers are adenocarcinomas, meaning they began in gland cells. Prostate tumors grow slowly and may not be diagnosed until later in life (over the age of 65). In some cases, this cancer remains asymptomatic during a person’s entire lifetime.

Prostate cancer is treatable if detected early. However, aggressive or advanced forms of the cancer can spread to other organs (metastasize), or lead to erectile dysfunction and incontinence.

 

Causes and Risk Factors

During each round of cell division random errors, or mutations, can occur in the DNA of prostate cells. While some mutations are inconsequential, others allow cells to escape the mechanisms that control cell growth, leading to tumor formation. While the detailed mechanisms leading to cancer onset are not known, the following risk factors increase the likelihood of developing the disease:

  • Age. Prostate cancer is common in men over the age of 40, with the majority of cases being diagnosed after the age 65.
  • Race and ethnicity. Prostate cancer is more common in African American men, and men of North American, Northwest European, Australian, and Caribbean Island nationalities.
  • Family history. A family history of prostate cancer is associated with a greater risk of developing the disease due to shared environmental and genetic factors. Inherited mutations in the HPC1 (hereditary prostate cancer gene 1), and BRCA1 and BRCA2 (breast cancer early onset genes 1 & 2) are linked to some prostate cancers. Mutations in the BRCA1 and BRCA2 genes are also linked to breast and ovarian cancers in women, therefore a family history of these cancers increases the risk of prostate cancer in male progeny.
  • Obesity. Men who are diagnosed with prostate cancer and have a high body mass index are more likely to have the aggressive form of the cancer.
  • Radiation. Prolonged exposure to radiation damages the DNA of cells and can increase the risk of all cancers, including prostate cancer.

Symptoms

The close proximity of the prostate with respect to the bladder, urethra, and the nerves of erectile function helps explain many of the prostate cancer symptoms. The list includes:

  • Frequent urination
  • Pain and difficulty while urinating
  • Interrupted and/or weak urine stream
  • Blood in the urine or semen
  • Pain in the hips, thighs, or lower back
  • Pain during an ejaculation
  • Erectile dysfunction.

Diagnosis

prostate lateral cross section showing urethraThe following tests are used to screen and diagnose prostate cancer:

  • Physical exam. During a digital rectal exam (DRE) a doctor inserts a finger inside the rectum to feel for the prostate gland located directly in front. Additional tests follow if bumps or hardened areas are detected.
  • Prostate-specific antigen (PSA) test. This blood test measures the amount of a prostate-protein called PSA. Elevated levels of PSA are associated with various diseases of the prostate, including prostate cancer.
  • Transrectal ultrasound (TRUS). A TRUS uses reflected sound waves to construct an image of the prostate for better visualization of possible abnormalities.
  • Biopsy. Depending on the results from other tests, a biopsy may be performed to collect a small sample of the prostate gland for further testing. This procedure is carried out by inserting a thin needle through the wall of the rectum to the adjacent prostate.

Following a positive diagnosis, various tests and imaging techniques are performed to “stage” the cancer and determine the extent of metastasis (or spread) beyond the prostate gland. Adenocarcinomas are typically staged from 1-4 (represented as Roman numerals I–IV).

  • Stage I: The cancer is present in a small area of the prostate gland.
  • Stage II: The cancer has spread to a larger area of the prostate, or may still be small but considered aggressive. 
  • Stage III: The cancer has spread to the seminal vesicles and neighboring tissues.
  • Stage IV: The cancer has spread to neighboring organs, to the lungs, or to other distant organs.

 

Treatment

Treatment options vary per case and depend on the patient’s age, overall health, symptoms, and cancer stage. Because prostate tumors grow slowly, some patients are monitored and never require actual treatment. The following treatments are available for prostate cancer:

  • Surgery. Early-stage prostate cancer can be removed – and often cured – using a surgical procedure called radical prostatectomy. A prostatectomy is performed by making an incision in the abdomen (retropubic surgery) or an incision between the anus and scrotum (perineal surgery). Less invasive laparoscopic methods (either manual or robot-assisted) that use a thin tube with a camera on the end (laparoscope) are also available.
  • Radiation. Radiation treatment uses high energy to kill cancer cells. The treatment is directed at the prostate either externally using X-rays and protons (external beam radiation), or internally by implanting radioactive pellets that deliver radiation inside the prostate (brachytherapy). Radiation therapy is often used with other treatments to destroy remaining cancer cells or shrink the tumor.
  • Hormone therapy. Prostate cells require the male hormone testosterone to flourish; thus hormone therapy removes testosterone to slow tumor growth. Luteinizing hormone-releasing hormone (LH-RH) agonists block testosterone production in the testicles. Alternatively, removing the testicles by surgery (orchiectomy) may halt testosterone production faster than LH-RH agonists. Anti-androgens inhibit the function of testosterone by blocking their binding sites on proteins called receptors. Hormone therapy can be used to shrink tumors. It is also used when surgery and radiation therapies are ineffective or not an option.
  • Cryoblation. As an alternative to radiation, cryoblation is used to kill cancer cells with cycles of freezing and thawing. In this procedure, cold and hot gas is delivered to prostate tissue using a thin needle inserted into the prostate.
  • Chemotherapy. Advanced prostate cancer that has spread to distant organs can be treated with chemotherapy, which is a systemic treatment to kill rapidly dividing cells, such as cancer cells. Chemotherapy is usually used when hormone therapy is not effective.
  • Immunotherapy. Custom vaccines (Provenge®) that help the body’s immune system fight prostate cancer are available on a made-to-order basis. The vaccines are made by removing white blood cells from the patient and training them to recognize and destroy prostate cancer cells. The reprogrammed cells are then reintroduced into the same patient. This treatment is costly and used in rare cases for advanced prostate cancers.
  • Experimental therapies. Advanced cancer patients who are not responding to available therapies may consult their doctors about available clinical trials for treatments not yet approved by the Food and Drug Administration (FDA).

Prevention

Men can reduce their risk of prostate cancer by eating a healthy diet and exercising regularly. Some medical organizations recommend routine prostate cancer screening for men over the age of 40. Those with a family history of prostate, breast, and ovarian cancers can discuss screening options for prostate cancer with their doctor.

Sources

  • “What is Prostate Cancer”. American Cancer Society. Mar 2014. Retrieved Jul 13, 2014. http://www.cancer.org/cancer/prostatecancer/detailedguide/prostate-cancer-what-is-cancer.
  • "Prostate Cancer". Mayo Clinic. Mayo Foundation for Medical Education and Research. Aug 2013. Retrieved Jul 13, 2014. http://www.mayoclinic.org/diseases-conditions/prostate-cancer/basics/definition/con-20029597.
  • "Understanding Prostate Cancer”. Prostate Cancer Foundation. Retrieved Jul 13, 2014. http://www.pcf.org/site/c.leJRIROrEpH/b.5802023/k.B322/About_the_Prostate.htm.
  • “Prostate Cancer”. National Cancer Institute. NIH. Retrieved Jul 13, 2014. http://www.cancer.gov/cancertopics/types/prostate.