In what amounts to the discovery of another mystery about breast cancer, Swedish and American researchers have concluded that--for reasons still unidentified--victims who are 45 to 49 when their cancers are diagnosed stand a markedly better chance of surviving than either younger or older women.
And while other scientists who have noted the possible association between age at the time of diagnosis and survival have speculated that greater longevity among such women may be due to body chemistry changes that come with menopause, the Swedish research team says its analysis disproves that connection.
Moreover, the relative survival advantage or disadvantage that is accorded by a woman's age at diagnosis remains with her for her entire life. A woman who is 30 when her cancer is identified remains at far greater risk of dying from the disease than a woman diagnosed in her 40s, and women who are 45 to 49 when diagnosed apparently never lose their increased survival benefit.
What is clear from data accumulated in a nationwide Swedish cancer registry and a U.S. government-funded data collection program in the San Francisco Bay Area, however, is that women who are in their fifth decade of life when they are diagnosed--especially those 45 to 49--die from breast cancer significantly less often than women in any other age bracket.
Breast cancer is one of the deadliest forms of the disease for women, with 119,900 new cases reported in 1985 and 39,900 deaths nationwide projected for 1986, according to the American Cancer Society. (Breast cancer has recently been surpassed by lung cancer as a killer of women.) Its causes remain unidentified.
Both the Swedish analysis, conducted by a team of doctors at University Hospital in Uppsala, and the American study, at the Stanford University School of Medicine, agree in their analysis of the degree of survival advantage for women by age range. The Swedish team, headed by Dr. Hans-Olov Adami, had earlier published several analyses of data from the same 58,000 Swedish women whose cases were scrutinized in the latest report.
Results of studies by the Swedish and American groups are being published today in the New England Journal of Medicine. Both reports come as new developments in a field in which U.S. researchers are not considered among the world's best. Papers published in the field in recent years have come from Sweden, Norway, South Africa, Australia and even the Soviet Union, but seldom from American research centers.
A member of the Swedish team, speaking by phone from a cancer conference in Hungary, said the Uppsala researchers have also recently found an unexpected correlation between women who contract breast cancer and the incidence of cancer of the uterine lining--called the endometrium.
For women of middle age and older, Dr. Ingemar Persson said, there appears to be some possible "common factor" that causes both breast and endometrial cancer. Persson said the Swedish team presented its endometrial cancer data for the first time earlier this week at the 14th International Cancer Congress in Budapest.
If the precise chemical mechanism responsible for the unexplained higher survival rates in women in their mid- to late 40s could be identified, doctors might--at least theoretically--be able to use it to alter breast-cancer susceptibility in women in other age brackets. But since the chemical process in question remains unidentified, it is uncertain whether such a development may ever occur.
Adami, who was also attending the Budapest conference, said the Swedish team had not expected to find a specific age bracket--especially the one eventually discovered--with superior survival rates. "I think the most surprising finding was the very rapid decrease (in survival rates) at younger and at early postmenopausal (50 and above) ages," Adami said in a separate telephone interview. "There is no reasonable biological explanation available."
Persson noted, moreover, that the significance of age at the time of diagnosis probably has little to do with the effectiveness of breast cancer detection programs but is the result of some idiosyncrasies of body chemistry that change with age but whose actions, for the moment, remain a complete mystery.
Young Women at Risk
Doctors have recognized for several years that young women--those 30 to 35 and under--who get breast cancer have poor prognoses. The Stanford team, agreeing with a variety of previous studies, said poor survival rates in such young Bay Area women may be influenced by the unique hormone changes that occur in the body at the time of pregnancy. Because a higher proportion of women in their 20s and 30s become pregnant than do older women, the pregnancy chemistry influence may skew average breast-cancer rates for all younger women.