Lower-income women appear less likely to survive breast cancer than their more-affluent counterparts, and later diagnosis may largely explain why, a new study suggests.

Using data on more than 100,000 U.S. women diagnosed with breast cancer between 1998 and 2002, the study found that those living in economically depressed areas had poorer survival rates through the end of 2005.

When socioeconomics were considered alone, women in the poorest areas were almost one-third more likely to die during that period than those living in the highest-income areas.

When other factors were weighed, the timing of a woman’s diagnosis seemed to explain much of the income gap, according to findings published in the online journal BMC Cancer.

Lower-income women were more likely to be diagnosed at a later stage: 13 percent of those in the two lowest-income areas were diagnosed after the cancer had spread beyond the breast, compared with just under 10 percent of women in the two highest-income areas.

Past studies have shown that women with lower incomes and less education have, on average, poorer breast cancer survival rates.

These latest findings suggest that later diagnosis may largely explain why, according to study author Dr. Xue Qin Yu, a researcher at Cancer Council New South Wales, in Kings Cross, Australia.

However, lower rates of recommended treatments were also a factor, Yu told Reuters Health in an email.

The study found that women in lower-income areas were less likely to receive radiation as part of their first course of treatment: 55 percent to 58 percent of women in the two higher-income groups received radiation, versus 48 percent in each of the two lower-income groups.

Radiation is typically recommended to destroy any remaining cancer cells after a breast tumor, or the breast itself, has been surgically removed.

Exactly why there were income-related treatment differences is unclear. But lack of insurance or poorer overall health among lower- income women could be at work, Yu writes - as could bias on the part of doctors, or higher rates of treatment refusal among poorer women.

Race also seemed to make a “modest” contribution to the connection between socioeconomics and breast cancer survival, Yu found.

Just under 80 percent of black women were alive one year after diagnosis, versus roughly 90 percent of women of other races. Much of the racial gap seemed to be explained by differences in diagnosis and treatment, but not all of it; biological factors might play a role, Yu notes, but it is not possible to tell from this study.

According to Yu, the findings point to a need for “targeted interventions” to increase breast cancer screening and early treatment of lower-income women.

That, the researcher said, could include education for women and more government funding of screening programs for low-income or uninsured women.

SOURCE: BMC Cancer, online October 13, 2009.