In an effort to better understand these diseases, Council staff conducted independent research. This section discusses staff research on the prevalence, prevention, treatments, and risk factors associated with prostate cancer and colorectal cancer.
Prostate cancer is the most common malignancy (excluding skin cancer) and the second leading cause of cancer deaths among men in the United States. It accounts for 32% of all male cancers and 14% of all male cancer-related deaths. According to the American Cancer Society, the lifetime risk of developing prostate cancer is 1 in 5 for American men.
According to the Pennsylvania Department of Health, there were 9,432 cases of prostate cancer diagnosed in Pennsylvania in 1995. The age-adjusted incidence rate of prostate cancer in Pennsylvania was 132.6 per 100,000. The incidence rate for black men (249.6 per 100,000) was twice the incidence rate for white men (123.6 per 100,000). The Department of Health states that over 80 percent of all cases of prostate cancer reported in 1994 were diagnosed at the localized stage of disease.
The American Cancer Society estimates that in 1998, prostate cancer will be the second most diagnosed cancer in Pennsylvania with 10,400 new diagnoses, an estimated 15% of new cancer diagnoses in Pennsylvania. According to the American Cancer Society, in 1998, prostate cancer will be the fourth leading cause of cancer deaths in Pennsylvania, representing 2,200 deaths, nearly 7% of all cancer deaths.
It should be noted that prostate cancer incidence rates increase significantly with age. Prostate cancer is rare among men under age 40, with an incidence rate of less than 1 per 100,000 men. The rate climbs to 82 per 100,000 for men ages 50-54, 518 per 100,000 for men ages 60-64, and 1,326 per 100,000 for men ages 70-74. The American Cancer Society estimates that more than 75% of all prostate cancers are diagnosed in men over age 65. As Pennsylvania's population is increasingly elderly, the prevalence of prostate cancer is of real concern.
The American Cancer Society estimates that there will be 7,900 cases of colorectal cancer diagnosed in Pennsylvania in 1998 and 3,400 deaths resulting from colorectal cancer; this represents over 11% of new cancer diagnoses in Pennsylvania and almost 11% of cancer-related deaths. Although colorectal cancer will be the fourth leading cancer diagnoses, it will be the second leading cause of cancer-related deaths in Pennsylvania. The American Cancer Society estimates that colorectal cancer will strike one in 17 Americans.
There is good news concerning colorectal cancer, however. Nationally, the incidence rates have declined in recent years from a high of 53 per 100,000 in 1985 to 45 per 100,000 in 1993. The American Cancer Society states that "the recent decline may be due to increased sigmoidoscopic screening and polyp removal, preventing the progression of polyps to invasive cancers."
The major risk factors for prostate cancer are age, race, and family history. As previously discussed, the incidence of prostate cancer increases dramatically with age. According to the American Cancer Society, African-American men have the highest prostate cancer incidence rates in the world. Furthermore, "recent genetic studies suggest that an inherited predisposition may be responsible for 5% - 10% of prostate cancer."
Unfortunately, since the major risk factors for prostate cancer (age and race) are uncontrollable, there is no effective method of prevention for prostate cancer. The American Cancer Society, however, states that consumption of lycopene, an antioxidant found in tomatoes and tomato-based products, may be associated with a decreased risk.
Prostate cancer symptoms include: weak or interrupted urine flow, inability to urinate or difficulty starting or stopping the urine flow, frequent urination, blood in the urine, painful or burning urination, and continuing pain in lower back, pelvis, or upper thighs. The American Cancer Society notes, however, "most of these symptoms are nonspecific and may be similar to those caused by benign conditions such as infection or prostate enlargement."
The major risk factors for colorectal cancer include a personal or family history of colorectal cancer, polyps, or inflammatory bowel disease; physical inactivity; a high-fat and/or low-fiber diet; and inadequate consumption of fruits and vegetables.
A low-fat and high-fiber diet is reportedly one's best method of protection against colorectal cancer. Recent studies also suggest that estrogen replacement therapy in post-menopausal women and non-steroidal anti-inflammatory drugs such as aspirin may reduce colorectal cancer risk. As with prostate cancer, the major risk factor, family history, is unalterable.
Colorectal cancer symptoms include rectal bleeding, blood in the stool, and change in bowel habits.
The main screening tests for prostate cancer are the digital rectal examination and the prostate-specific antigen test. The digital rectal examination is the traditional method for screening; it involves a physician palpating the prostate through the wall of the rectum. The prostate specific antigen test is a blood test which measures the level of a specific protein.
For positive digital rectal examinations and prostate specific antigen tests, the typical follow-up procedures are the transrectal ultrasound and transrectal needle biopsy. The ultrasound is often used to determine where tissue samples are to be taken from during a biopsy. For the biopsy, a physician inserts a needle into the prostate through the wall of the rectum and withdraws samples of tissue, which are tested for the presence of cancer.
The Council notes that the Food and Drug Administration has recently (March 1998) approved a new blood test for prostate specific antigen called the "free" prostate specific antigen test. As recently reported in the Philadelphia Inquirer, "A new blood test for prostate cancer could eliminate 120,000 needless biopsies a year in the United States, researchers say." "The new test, approved by the government in March, measures the blood levels of "free" prostate-specific antigen, a protein produced by the prostate gland. The traditional PSA [prostate specific antigen] test, used since the early 1990s, measures the protein in a different form when it is chemically bound to another substance." "The new test does not replace traditional PSA [prostate specific antigen] testing; it is given as a follow-up when the traditional PSA [prostate specific antigen] test yields uncertain results." Since the approval of the new test is a recent development, it is difficult to ascertain the impact it will have on follow-up testing, although the preliminary evidence is optimistic.
The digital rectal examination has many inert flaws. By definition, Stage A tumors are non-palpable, meaning that a digital rectal examination will not detect them. In addition, the examiner can only palpate certain areas. One study estimated that 25% - 35% of tumors occur in portions of the prostate not accessible by palpation. Studies cite the sensitivity level of the digital rectal examination at anywhere from 18 to 68%. Furthermore, the digital rectal examination produces a large number of false positives. The positive predictive value (the probability of cancer when the test is positive), in asymptomatic men ranges from 6-33%. This means the majority of positive digital rectal examinations are non-cancerous. Another study reported that 25% of men presenting with metastatic disease have normal prostate examinations. This suggests that while healthy men may receive a positive digital rectal examination, for some men with advanced stages of prostate cancer the digital rectal examination provides false negatives.
A prostate specific antigen test is the other main type of prostate cancer screening. Unfortunately, there is not a definite measure which constitutes a significantly high prostate specific antigen level. The American Cancer Society defines an abnormal prostate specific antigen as a value of above 4.0 ng/ml, however, at this level 21% of patients with benign prostatic hyperplasia have elevated prostate specific antigen concentration and may therefore undergo an unnecessary biopsy. Furthermore, at a prostate specific antigen level of 4.0 ng/ml, 30% of all known prostate-confined malignancies remain undetected. Some sources suggest that by raising the limit for an abnormal prostate specific antigen to 10.0 ng/ml, the amount of false positives can be reduced; this will, however, be accompanied by an increase in the number of false negatives. The prostate specific antigen test appears to have a lower probability of a false positive than the digital rectal examination, although the positive predictive value is still only 28-35% (roughly meaning that only one in three positive prostate specific antigen tests is actually cancer). The false positives associated with prostate specific antigen tests can be the result of conditions such as hypertrophy and prostatitis.
The prostate specific antigen test is effective in detecting some cases where the digital rectal examination is negative. Therefore, the combination of a digital rectal examination and a prostate specific antigen test is the most successful method of detecting prostate cancer. In one study, the combination of an elevated prostate specific antigen and abnormal digital rectal examination achieved a 49% positive predictive value. In other words, when both the digital rectal examination and prostate specific antigen showed positive results, cancer was present in about one of every two cases.
The large number of positive digital rectal examinations and prostate specific antigen tests correspond to a large number of biopsies. One study found that 18% of the screened population will undergo a needle biopsy. It is likely, however, that the introduction of the "free" prostate specific antigen test will reduce the number of biopsies. As discussed, a significant percentage of positive digital rectal examinations and prostate specific antigen tests are false positives, suggesting that many of these biopsies are unnecessary.
While the large number of false positives and needle biopsies produced by both digital rectal examinations and prostate specific antigen tests is a concern, there is more concern over the treatment options for patients with prostate cancer. Prostate cancer is a slow growing-cancer. Because of the nature of the disease, a structured literature review concluded that the median annual rates of metastatic disease (cancer which spreads to other parts of the body) and prostate cancer mortality were 1.7% and 0.9%, respectively, without treatment.
Because the rate of metastasis is relatively low, treatment deferral, known as watchful waiting or expectant management, is a popular option for many men. In expectant management, the cancer is monitored for any changes, but no immediate treatment is undertaken. Reported 10-year disease-specific survival for expectant management of palpable but clinically localized prostate cancer is 84%-96%.
The American Cancer Society reports that the average five-year relative survival rate for prostate cancer is 89%. If the cancer is localized, the survival rate is 100%. For prostate cancer with regional metastasis the survival rate is 94%; for distant metastasis, it is 31%. According to the American Cancer Society, the most recent data shows that 67% of men diagnosed with prostate cancer survive 10 years and 50% survive 15 years.
When patients do choose to undergo treatment, there are limited options. The most common active treatments include surgery, radiation, chemotherapy, and hormone therapy. The most common types of surgery are radical prostatectomy and transurethral resection of the prostate.
A prostatectomy is the surgical removal of the prostate and some of the surrounding tissue. This is typically performed if the cancer is confined to the prostate. The operation lasts for two to four hours and has an in-hospital recovery time of three to seven days. In most cases, a catheter is inserted after surgery and remains in place for two to three weeks. Transurethral resection of the prostate, the other form of surgery, is the surgical removal of part of the prostate. It is used for men who cannot undergo a radical prostatectomy because of age or other conditions; transurethral resection is not expected to remove all of the cancer.
For the patients who opt for prostatectomy, the side effects, including impotence and incontinence, are of real concern. One study of Medicare patients revealed that of patients who underwent radical prostatectomy, 30% used pads to control wetting, 60% reported partial erection, 15% were treated for sexual dysfunction, and 20% had surgical procedures for strictures. Another study found that only half of men undergoing treatment (either prostatectomy or radiation) for Stages B, C, or D prostate cancer had no adverse effects.
Radiation uses x-rays to kill cancer cells. It is used in treating prostate cancer which has spread, as well as localized cancer. Side effects of radiation include impotence and incontinence. Hormone therapy is used for patients whose cancer has spread to other parts of the body. Hormone therapy can involve removal of the testicles, injections of drugs which decrease testosterone production, and the use of anti-androgens (drugs which block the body's ability to use testosterone). Again, impotence is a side effect, as is decreased sexual desire. Chemotherapy is used primarily in those patients where the cancer has spread and hormone therapy has failed; it is not an effective treatment against early prostate cancer. Chemotherapy's side effects include nausea, hair loss, anemia, and reduced ability of blood to clot.
The American College of Physicians puts forth a simple theory. They maintain that, "Screening should not be recommended for men who are unwilling to consider aggressive treatment if a tumor of potential clinical significance is found or who are not candidates for such therapy."
The fecal occult blood test is the most popular and least expensive test for colorectal cancer. A fecal occult blood test is an examination of a stool sample for blood. Fecal occult blood tests yield numerous false positives including bleeding due to hemorrhoids, diverticulitis, and peptic ulcers. The reported positive predictive value (the probability of cancer when the test is positive) of fecal occult blood tests for persons over age 45 is only 12% to 17%. Furthermore, a person who receives annual fecal occult blood tests from age 50 to 75 has an estimated 45% probability of receiving a false-positive result.
Another type of screening procedure is a sigmoidoscopy, in which a lighted tube is placed in the rectum, allowing a physician to look for the presence of polyps (small growths which may become cancerous). There are two main types of sigmoidoscopes: rigid and flexible. The rigid sigmoidoscope is about 25 cm long, the short flexible sigmoidoscope is 35 cm long, and the long flexible sigmoidoscope is 60 cm long. A flexible sigmoidoscopy is not only more comfortable than a rigid sigmoidoscopy, but it also has advantages in its length. The rigid sigmoidoscope can detect about 25% to 30% of colorectal cancers, whereas the long flexible sigmoidoscope can detect 65% to 75% of polyps and 40% to 65% of colorectal cancers. Sigmoidoscopies can yield false positives, detecting polyps that are unlikely to become malignant during the patient's lifetime.
If either test yields positive results, the next step is a colonoscopy in which a lighted tube is inserted through the rectum up into the colon. The tube is attached to a camera which allows the doctor to look for polyps. If a polyp is found, the doctor may remove it by using a wire loop to sever the polyp from the wall of the colon. The polyp can then be sent to a lab to see if cancerous cells are present. One physician estimated that 32% of the annually fecal occult blood screened population underwent a colonoscopy during a 13-year follow-up period.
Surgery is the main treatment for colorectal cancer. The usual operation is a segmental resection in which the cancer, some surrounding tissue, and nearby lymph nodes are removed. The remaining sections of the colon are then attached back together. Occasionally, a colostomy (creation of an abdominal opening for the elimination of body wastes) is needed as a surgical treatment. Chemotherapy or a combination of chemotherapy and radiation is given to patients whose cancer has deeply perforated the bowel wall or spread to the lymph nodes.
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