Frequently Asked Questions
How common is cancer?
Cancer is very common in California, the United States, and in most other developed countries. In the Greater Bay Area, more than 30,000 people are diagnosed every year with some form of invasive cancer, not including the common basal and squamous skin cancers. Based on current statistics, more than two out of every five Californians will develop cancer at some time in their lives, and about one in 340 children will be diagnosed with cancer before age 20 (California Cancer Facts and Figures, 2009). Many cancers are now curable and cancer treatment continues to improve. Nonetheless, nearly one out of five Californians dies from cancer.
Which types of cancer are most common?
There are many different kinds of cancer, depending on where in the body the cancer starts and the type of cell involved. The four most common types are: prostate, breast, lung, and colorectal cancers. Out of every twenty cancer diagnoses, about three will be breast cancers, three will be prostate cancers, three will be lung cancers, and two will be colorectal. There will be about one in the bladder or kidney, one in the ovary, uterus or cervix, and one will be a lymphoma. The remaining six will include a variety of types, such as melanoma, leukemia, cancers of the mouth and throat, pancreas, stomach and many others.
How common is skin cancer?
This depends on the type of skin cancer. The American Cancer Society estimates that approximately one million basal and squamous cell carcinomas of the skin will have been diagnosed in the US in 1998, compared with a total of 1.23 million invasive cancers of all other types combined. Precise information on the incidence of basal and squamous cell carcinomas is very difficult to collect because these cancers are mostly diagnosed and treated in doctors' offices and rarely lead to serious disease. For these reasons, information on basal and squamous cell cancers is not collected by most cancer registries.
The other type of skin cancer that commonly occurs is melanoma. Data on melanomas are collected by most cancer registries, as it is the skin cancer that is most likely to metastasize (spread) to other parts of the body. Melanomas were the fifth most common cancer diagnosed overall among non-Hispanic white males in the Greater Bay Area during the period 2000-2004.
Who gets cancer?
Unfortunately, almost anyone can develop cancer, even children and young adults who lead active, healthy lives. However, nearly 60 percent of the cancers diagnosed in California are among people 65 and older, who make up only about 10 percent of the population. Surprisingly, there are large differences among people of different ethnic origins. Generally, African American men have the highest cancer risk, and non-Hispanic white people have substantially higher cancer rates than persons of Latino or Asian origin. Childhood cancer rates are similar across ethnic groups.
How many people currently have cancer?
The current estimate in the recent California Cancer Facts and Figures is that more than 950,000 Californians alive in 2007 have a history of cancer, not including basal or squamous cell carcinomas of the skin or certain non-invasive cancerous conditions of the uterine cervix. Many of these individuals have no further evidence of the disease, and have the same life expectancy as people who have never been diagnosed with cancer.
What causes cancer?
It is rarely possible to find the cause of a cancer in an individual, but studies on groups of people with cancer have shown specific risk factors to be associated with specific cancers. This suggests that different types of cancer probably have different causes. These studies also indicate that cancer formation is a multi-step process ('multi-factorial'), and that for most cancers the time from a cancer-causing exposure to a clinically diagnosable cancer averages about 20 years.
Among the known risk factors for cancer, tobacco stands out. Cigarette smoking is associated with more than 85 percent of all lung cancers, and with a substantial proportion of cancers of the bladder, mouth and throat, stomach, pancreas and others. Diet is also a risk factor; higher cancer rates are seen in people who eat a diet high in fat and low in fresh vegetables and fruits. It is estimated that diet and tobacco together account for approximately two out of three cancers.
Breast cancer is the most common cancer among women. About 50 percent of breast cancers are thought to be explained by known risk factors such as a family history of cancer and hormonal functions associated with early onset of menstruation and late menopause, delayed childbearing and having fewer children. Few risk factors have been defined for the most common cancer in men, prostate cancer.
Occupational studies have shown certain chemicals and other substances to be carcinogenic; these include asbestos, benzene, arsenic, vinyl chloride and other industrial products. Exposure to these substances is thought to account for about 5 percent of all cancers.
Are cancer rates in the Greater Bay Area going up?
No! Overall cancer incidence and mortality rates have continued to decline in the Greater Bay Area, in large part due to declines in tobacco-related cancers in males and increased use of cancer screening tests in females. Incidence rates for invasive breast cancer declined sharply in most racial/ethnic groups for the years 2003 and 2004. Work is ongoing to see if these declines are temporary and if they relate to the stoppage of hormone replacement therapy by many women after the July 2002 announcement by the Women's Health Initiative that estrogen/progestin hormone therapy increases the risk of developing breast cancer and heart disease.
However, even if the rates of cancer change very little, the total numbers of people who develop cancer will increase as the population gets older. This demographic change, combined with the fact that more people are surviving from cancer and that people are discussing cancer more readily, may have contributed to the widespread impression that the risk of developing cancer has recently increased.
How common are cancer clusters?
Cancer clusters are rare and usually due to chance. In only 5-15% of reported cancer clusters statistical testing confirm the number of observed cases exceeds the number of expected. Those investigations that do find an excess of cancer cases usually are unable to identify a specific environmental cause.
For more information about cancer clusters please download our newsletter Greater Bay Area Cancer Registry Report and visit the California Cancer Registry's Frequently Asked Questions about Neighborhood Cancer Concerns webpage. If you still have questions or concerns after reading the newsletter, please contact Kari Fish, Epidemiologist/Data Release Coordinator, at kari.fish@nccc.org, or call 510-608-5036.
How can I find out more about a particular cancer?
There are many cancer resources available by phone and online. Two that are renowned for their high quality include the National Cancer Institute's Cancer Information Service at 1-800-4-CANCER ( 1-800-422-6237), and the American Cancer Society (1-800-ACS-2345).
How can I enroll in a clinical trial for cancer treatment?
Information on clinical trials is available from the National Cancer Institute's Cancer Information Service at 1-800-4-CANCER (1-800-422-6237), and from their Comprehensive Cancer Database website.
How did a cancer researcher get my name and phone number?
A cancer researcher may have obtained your name and phone number from a hospital or facility where you were treated for cancer, or by applying to the Greater Bay Area Cancer Registry (GBACR). The state law mandating the California Cancer Registry requires that the information gathered be used solely for research into the causes and cures for cancer. Some research requires contacting patients to get information about their past histories. The GBACR provides patient contact information to researchers only under strict procedures. Patient identity is disclosed only to researchers who are conducting projects meeting stringent requirements for scientific merit and for handling of confidential information, and whose research has been approved by a federally authorized committee that oversees the protection of human subjects (Institutional Review Board).
What can I do to lower my risk of developing or dying from cancer?
Scientists still have much to learn about the causes of cancer, but in the meantime, it is prudent to follow these guidelines:
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Don't smoke, dip or chew tobacco and discourage young persons from starting tobacco use.
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Eat at least 5 servings of fresh fruit and vegetables per day.
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Cut down on the amount of fat in your diet.
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Limit the amount of alcohol you drink.
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Try to get some exercise every day.
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Protect yourself from the sun and avoid sunburns.
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Women need to examine their breasts once a month, as well as get regular breast examinations, mammograms, and Pap smears.
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Men should examine their testes regularly.
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Discuss with your doctor the advisability of colorectal cancer screening.
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Discuss with your doctor the advisability of being tested for hepatitis B or C infection. If you are not protected against hepatitis B virus, get vaccinated. If you are positive for either hepatitis B or hepatitis C virus, get screened regularly for liver cancer.
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Ask your doctor for other specific recommendations, particularly if you have a family history of cancer.
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