Changes in Breast Cancer Mortality Rates
In the United States as a whole, breast cancer mortality rates have declined somewhat in recent years. That this is a recent trend is evident from the fact that during the twenty years from 1970–1990, death rates showed a small but significant increase for white women of about 0.3 percent per year and a more substantial increase of 1.6 percent for black women.
During the 1990s, however, mortality rates fell in white women by 2.5 percent a year, while they declined more slowly in black women, at a rate of 1.0 percent. The decline in mortality has largely been attributed to broader screening leading to earlier stage at diagnosis, so it is understandable that access to and utilization of screening and treatment has been hypothesized as the major reason for these disparities in mortality. However, as we will see, the data on changes in incidence and mortality suggest that changes in treatment, not early detection, may play a more important role in explaining the recent decline in mortality.
In California, the decline has exceeded the national rate, but again, not for all racial/ethnic groups. For the years 1970 through 1999, the overall decline of 26 percent in mortality from breast cancer in California was seen mostly among white women. Mortality in white women decreased some 24 percent over this period, while it decreased only moderately in Hispanic women (4.8 percent). In black women, the rate stayed the same, with only a 0.4 percent decrease, while in Asian/Pacific islanders an increase in mortality of 78.4 percent was seen. It should be noted in the latter case, however, that even after this dramatic increase, the mortality rate for Asian/Pacific Islanders was 13.7 percent in 1999, far below the rates for other groups: 31.8 percent for black women, 26.8 percent for white women, and 17 percent for Hispanic women.21 However, this alarming rise in incidence in Asian/Pacific Islanders should be researched to understand which sub-groups are affected, and what factors seem to be involved.
An analysis of more recent changes in mortality rates from breast cancer in California shows declines in all racial/ ethnic groups. The annual percent decrease in mortality in the period from 1988–1999, was 2.5 percent for white women, 1.8 percent for black women, 1.6 percent for Hispanic women, and 1.0 percent for Asian/Pacific Islander women.
In the United States, current thinking appears to lend more weight to mammography screening and earlier diagnosis as the primary cause for decreasing mortality rates, while in the UK and in Europe, where mortality rates have been declining more recently, the predominant current theories seem to favor the wide use of adjuvant tamoxifen as the cause. Since tamoxifen lowers mortality by nearly a third in long term studies of women with ER-positive breast cancers (about 75 percent of those diagnosed) this is certainly a plausible explanation.
Looking at the changes in actual rates of incidence by stage and in mortality rates in breast cancer offers a surprising glimpse at the real impact of screening during the fifteen-year period between 1983 (before widespread screening was adopted) and 1998.
A 2002 article in the New York Times,22 in which Dr. Barnett Kramer, director of the Office of Disease Prevention at the National Institutes of Health, was interviewed, detailed the dramatic increase in breast cancer incidence, using the numbers in the Table 3, below. “There are very few things that can so dramatically increase the incidence of new disease,” Dr. Kramer said, emphasizing that there is no apparent cause, in the form of a strong new carcinogen, like tobacco, to explain this 27 percent increase in incidence over fifteen years. “That”, he said, “leaves screening as an explanation,” Dr. Kramer continues. “Mammography appears to find many cancers that would not otherwise have been found in a woman's lifetime.”
Indeed, the data on changes in stage at diagnosis and changes in death rates offer an illuminating picture. Looking at the increases and decreases in stage at diagnosis, by comparison with the decrease in death rates, in Table 3, it becomes quite clear that while we may be reducing stage at diagnosis and deaths a modest amount, we are, in the process, diagnosing many more early-stage cancers that are likely never to progress to become life-threatening.
Table 3. Changes in Stage at Diagnosis and Deaths
from Breast Cancer
(SEER Data United States, 1983–1998)
“This phenomenon is largely attributable to mammography,” according to the New York Times article: “The number of women with breast cancers with the worst prognosis, those that spread to other organs, had been fairly constant in the years before mammography was introduced, and that trend did not change after the introduction of mammography.”
Clearly, Dr. Kramer was suggesting that early detection had failed to live up to its promise. “If screening worked perfectly,” the article continues, “every cancer found early would correspond to one fewer cancer found later. That, he (Kramer) said, did not happen. Mammography, instead, has resulted in a huge new population of women with early stage cancer but without a corresponding decline in the numbers of women with advanced cancer.” The modest size of the reductions in later stage cancers and the unchanged status of metastatic disease are troubling. It appears that the early-detection approach to reducing cancer mortality fails to take into account the reality that some tumors are so aggressive that even the earliest detection will fail to eradicate them, while others are so indolent that it seems to make little difference if they are found before they become palpable. The burden of advanced breast cancer shows no real sign of abating, and is likely to continue and even increase as treatments prolong life.
In Figure 7, the SEER data for 25-year breast cancer incidence rates by stage, as well as death rates, are presented in graphic form. The top line, representing localized breast cancer clearly shows the precipitous rise begun in the early 1980s, with the dashed reddish line indicating the trend. The other clearly ascending line, accompanied by a dashed reddish line, is for in situ breast cancer, also associated with increased mammography screening. The dashed purplish trendlines for both the regional breast cancer rates and deaths show only slight decreases. There has been no change in the rate of distant (metastatic) breast cancer diagnosed over twenty-five years.