The New York Times had an interesting piece awhile ago on a heated debate about the fact that women in their 80s and 90s aren't being urged to get mammograms on a regular basis:
As with most cancers, the risk of breast cancer increases with age. Yet while doctors tell women to have annual mammograms after age 40, they often advise 85-year-olds to go two or even three years between scans. The problem, doctors say, is too little data. Large clinical trials, including those that have found that mammography saves lives, tend to focus on younger people and exclude the very old. A recent study that tried to assess the usefulness of mammography among 80- and 90-year-olds found that very few women in this age group, 22 percent, underwent regular screenings for breast cancer, but that those who did were more likely to find the cancer early enough to avoid a mastectomy and survive at least five years.
The question is raised whether breast cancer screenings should really be a large focus when there are other more common physical conditions at that age to be looking out for, like heart disease or chronic pain. But considering the fact that two-thirds of people over 85 are women, some are saying it's just as important.
Another issue raised is that women over 74 years old haven't been studied in clinical trials on mammography, so organizations setting guidelines for older women have to use potentially inaccurate information because it's coming from research with younger subjects. In other words, the actual process of getting a mammogram or a biopsy may be a risk for women older than 80, particularly if they have other conditions like dementia or heart disease.
Check out the whole article, the read is worthwhile.