Welcome to the California Cancer Registry

Data & Mapping Tool

Data & Mapping Tool

Generate customized maps and tables of California cancer incidence or mortality rates.

Inquiry System


What do the maps show?

The maps show communities in California where the percentage of breast cancers diagnosed at an advanced stage is higher, lower or the same as the percentage in a comparison group. Only cases of breast cancer among women aged 40 years and older are included in these maps, because these are the cases that might have been detected through screening for breast cancer. The comparison group is made up of women who had the lowest percentage of breast cancers diagnosed at an advanced stage: white non-Hispanic women aged 40 years and older who live in high socio-economic status neighborhoods. Among women in this group, 28% of breast cancer cases were diagnosed at an advanced stage.

What don't the maps show?

The maps do not show:

  • the number of new cases of breast cancer
  • any of the risk factors for getting breast cancer,
  • the reason why women got breast cancer, or
  • why some communities have a higher percentage of advanced stage breast cancers than others.

What is breast cancer?

Breast cancer is a cancerous growth that starts from cells of the breast. The disease occurs mostly in women, but men can get breast cancer too. Because breast cancer is much more common in women, the maps include only female breast cancer. Breast cancer is the most common cancer among women in California. In 2008, more than 21,000 California women will be diagnosed with breast cancer, and more than 4,200 will die from the disease. Many breast cancers can be prevented through the use of regular screening tests including physical examinations and mammograms.

What is "advanced stage breast cancer"?

Advanced stage breast cancer refers to breast cancers that are diagnosed when the tumor has already spread beyond breast tissue to lymph nodes or other parts of the body. If breast cancer is diagnosed before the tumor has spread beyond breast tissue (i.e., "early stage breast cancer"), then almost 97 percent of women are expected to survive for 5 or more years after they are diagnosed. Among women whose breast cancer has already spread to nearby tissue or lymph nodes when it is diagnosed, about 79 percent are expected to survive for 5 or more years. Among women whose breast cancer has already spread to distant parts of the body when it is diagnosed, only 20 percent are expected to survive for 5 or more years.

How are the communities on the maps defined?

The communities on the maps are called Medical Service Study Areas, or MSSAs. The MSSAs were developed by the California Office of Statewide Health Planning and Development (OSHPD) to help identify communities that do not have adequate medical services. The MSSAs are made up of census tracts, and all MSSAs fall within county boundaries. There are 541 MSSAs in California. Since these MSSAs often represent a group of smaller communities or parts of larger communities, they allow for very specific information to be determined throughout the state.

How did you determine whether the percentage of advanced stage breast cancers in an area was higher, lower or about the same as the comparison group?

The street address for cases of breast cancer that were diagnosed among California women aged 40 years and older between January 1, 1999 and December 31, 2003 was coded to a census tract and county (a total of 97,933 cases). The percentage of advanced stage breast cancer cases was determined for each area, and for the comparison group. Then, the percentage of advanced stage breast cancer cases in each area was compared to the percentage of cases in the comparison group. Percentages were compared only for communities where there were at least 15 cases of breast cancer.

Why didn't you just map the number of women in each area who were diagnosed with breast cancer?

Some communities have a lot of women living in them; others have fewer women. Because of this, we cannot just compare the number of women diagnosed with cancer in each area. Generally speaking, communities with more women living in them will have more women with cancer. Those with fewer women will have fewer women with cancer. Also, because cancer is more common in older people, the age of the women who live in each area is important. Communities where older women live will have more cancer than neighborhoods where younger women live.

How did you determine which areas were significantly different from the comparison group?

A proportional incidence ratio (PIR) analysis was used to compare the proportion of advanced stage breast cancers diagnosed in each MSSA to the proportion in the comparison group. This analysis was able to adjust for differences in age distributions between the two groups, allowing for a more balanced comparison. The expected number of advanced stage breast cancers in each MSSA was calculated by multiplying the age-specific proportion of advanced stage breast cancers in the comparison group by the number of breast cancers diagnosed in the MSSA in each of the same age groups and summing to obtain the expected number for all age groups combined. Then, the PIR was calculated by dividing the observed number of advanced stage breast cancers by the expected number and multiplying by 100. A PIR value greater than 100 indicated that the proportion of advanced stage breast cancers in the MSSA was higher than in the comparison group. The PIR was determined to be statistically significant if there was a less than 5 percent probability that the result could be due to chance alone. In other words, there is good reason to believe that these areas actually do have higher than expected percentages of advanced stage breast cancer.

If my community has a high percentage of advanced stage breast cancers, what is the reason?

We don't know for certain. Usually, early stage breast cancers are found through cancer screening tests such as mammograms. If a community has a high percentage of breast cancers detected at advanced stage, it most likely means that fewer women in that community are having mammograms. This might happen for many different reasons. Perhaps there are many women in the community without insurance to cover the cost of screening. Or perhaps the community is in a rural area with fewer doctors, so screening is less available. Other factors such as lack of knowledge about testing, or fear of testing may also play a role. The maps show which communities may have less breast cancer screening, so that efforts can then be undertaken to try to determine what the reason is so that more women in the community can be screened and diagnosed early.

Am I more at risk for getting breast cancer if I live in a red or orange area?

No. If you live in an area shaded red or orange, it means that out of all the women in that area who do get breast cancer a lot more of them are found at advanced stage than in the comparison group. It doesn't mean there are more total cases of breast cancer in that area. Breast cancer risk depends on many things, including your age, lifestyle (smoking, diet, physical inactivity) and your family history.

Am I less at risk because I live in a green area?

No. If you live in an area shaded green, it means that out of all the women in that area who do get breast cancer there are fewer diagnosed at advanced stage than in the comparison group. It doesn't mean there are fewer total cases of breast cancer in that area. Breast cancer risk depends on many things, including your age, lifestyle (smoking, diet, physical inactivity) and your family history.

Will comparing cancer maps to maps of environmental risk factors show me what is causing communities to have a high percentage of advanced stage breast cancers?

No. These maps show where more women are having their breast cancers found at advanced stage compared to other communities, not where there are higher total rates of breast cancer. In other words, it is about whether a breast cancer is found earlier or later in its development, not whether the breast cancer develops in the first place. This has more to do with getting screened for breast cancer than with anything in the environment. A different kind of study would need to be done to learn more about all the possible environmental factors that might contribute to cancer causes.

Then how can the maps be used?

These maps can show us the pattern of advanced stage breast cancer across the state, help health officials plan services, and suggest areas for more research. They cannot, by themselves, tell us what causes breast cancer.

What can I do?

If you are concerned about your risk for getting breast cancer, there are things you can do. First, talk with your health care provider about your personal risk factors. Talk with your relatives about your family history of breast cancer. You should share this information with your health care provider. You may also want to find out about breast cancer screening programs that are available in your community and discuss them with your health care provider.