Long-Term Trends: Cases Up, Death Rate Down

More California Women Are Finding Out That They Have Breast Cancer

Each year, more California women are diagnosed with invasive breast cancer, the type of breast cancer that can spread to other body parts and lead to death. The number of cases is going up, and so is the rate per 100,000 women. Looking at the rate per 100,000 women is often more meaningful, because it allows comparisons over time and between groups of women. In 1973, about 115 out of 100,000 California women were diagnosed with invasive breast cancer. By 1999, the number had gone up to approximately 143.

More California women are also being diagnosed with in situ breast cancer, a localized tumor that does not spread to other parts of the body. In 1973, there were only about 6 cases of in situ breast cancer diagnosed per 100,000 California women. By 1999, there were approximately 32. Over time, some cases of in situ cancer will turn into invasive breast cancer, but others will remain harmless. There's currently no way to tell which in situ cancers will later cause harm, so physicians treat them all as potentially dangerous.

More Women Having Mammograms

Researchers believe one reason for the rise in the number of cases of breast cancer in California is that more women have mammograms yearly or every other year. The rates for both invasive and in situ breast cancer stayed almost the same from 1973 to 1982. Starting in 1982, many more women began to have mammograms regularly, and the rates for both types of breast cancer went up steeply. This trend lasted for about five years. The mammograms were allowing physicians to find tumors they otherwise would not have found until later or at all.

Since the mid-1980s, the rate for invasive breast cancer has gone up only a little, while the rate for in situ cases has continued to rise. This may be because more new groups of women have had their first mammogram.

However, there has also been a gradual, nationwide trend of breast cancer rates rising at about one percent per year for the past sixty years, suggesting that the actual incidence of breast cancer in California (after accounting for screening) is also increasing.

More California women are being diagnosed with breast cancer, a trend that started around 1982.

Figure 3

Breast cancer rates are fairly stable among white and African American women in California, but they are rising for Hispanic and Asian/Pacific Islander women.

The Death Rate is Dropping

Since 1988 the death rate for breast cancer in California has been dropping. The actual number of deaths has gone down only slightly, from 4,121 in 1988 to 4,039 in 1999, with a high of 4,404 in 1994, but because California's population continues to grow, the rate of death has dropped more steeply. In 1988, there were about 32 deaths per 100,000 California women from breast cancer. In 1999, the number had dropped to 24.5.

Death Rate Drop Varies by Ethnic Group

The breast cancer death rate has dropped more among women from some California ethnic groups than among others. The overall drop in the California breast cancer death rate is mostly due to a lower death rate among white women.

In 1988, the group with the highest death rate was African American women, with 39.9 deaths per 100,000. By 1999, the number was down to 31.8 per 100,000, but this was still the highest of any ethnic group in the state.

In 1988, the ethnic group with the lowest breast cancer death rate was Asian/Pacific Islander women. Their rate was only 12.6 deaths per 100,000. In 1999, the figure was still the lowest of any ethnic group, at 13.7 deaths per 100,000, but this is also the only group whose death rate rose between 1988 and 1999.

The 1988 death rate for white women was 35.6 per 100,000. In 1999, the rate was 26.8 per 100,000, the biggest improvement of the four ethnic groups.

The 1988 death rate for Hispanic women was 20.8 per 100,000. In 1999, it had dropped to 17 per 100,000.

Figure 4

Why the Death Rate Is Down

We don't really know why the death rate is down. Some scientists believe the death rate has dropped because more cases of breast cancer are being caught at earlier stages with mammograms. However, if this were the only reason, there would be a drop in the number of women diagnosed at later stages. But that number has not dropped. And at the same time, more and more women are going through the scare of an abnormal mammogram, requiring a biopsy that, more often than not, is benign.

There are other possible reasons that may provide part or all of the explanation for the drop in the death rate. First, breast cancer is being treated more aggressively. Second, treatment has improved, especially for women whose tumors are found at an early stage. Third, more women are receiving treatment. Meanwhile, more and more women who would have done fine without more treatment are unnecessarily getting more treatment, with all of its side effects.

Age-Adjusted Breast Cancer Rates

The figures in this section are adjusted for age. Adjusting for age allows the rates to reflect what they would be if all ethnic groups in California had the same age distribution. Older women are more likely to get breast cancer. Adjusting for age means that the differences between the ethnic groups are not due to one group containing more older women than another. Age adjustment also means that the differences between the years compared here are not due to there being more older women in California during some years than others.

How This Research Was Done

Researchers used information from the National Cancer Institute, the California Cancer Registry, and death certificates filed in California. For more information on the Registry, and on why the information stops in 1999, see the introduction to this booklet. A woman whose cancer recurs is only counted once in these statistics. However, a woman who has already had breast cancer, and who also later develops a new tumor that lab analysis shows is not the result of her previous tumor, counts as two cases. Information in this section comes from Chapter 5 of Breast Cancer in California, 2003, “Trends in Female Breast Cancer Incidence and Mortality in California,” by Kumarss Nasseri, D.V.M., Ph.D., M.P.H.