How effective are screening tools in reducing mortality from certain cancers?

As I work on an article from my dissertation, I've been thinking about one scholar's challenge to the pap smear. Ilana Lowy, a fantastic historian/social scientist of medicine, argues that the pap smear may not be the reason for the reduction in cervical cancer mortality. Now, the NYT also briefly mentions a BMJ article that suggests mammograms are not the cause for declining rates of breast cancer mortality.

These women's health screenings have been considered essential, if sometimes problematic, methods of improving health outcomes. Adele Clarke and Monica Casper have written about the networks and many processes that go into cervical cancer pathology screening, noting all the actors, tools, and challenges for pathologists who read hundreds of cervical cell slides in a day. Public health has long considered the gynecological method of the pap smear to be a "gold standard" of screening, as it's a relatively cheap and effective way to purportedly reduce cervical cancer deaths. Indeed, since the institutionalization by gynecological associations of regular pap smears in the U.S., deaths due to cervical cancer have dropped radically. As a non-laboratory scientist, I've been persuaded that the pap smear, while imperfect, was really a meaningful intervention. Conversely, I've also been long concerned about the practices associated with gynecology. Terri Kapsalis has a fantastic set of essays in her book about some of the ongoing and historical problems with gynecological practice. At a recent conference, Lowy emphasized her skepticism about the efficacy of the pap smear. Based on epidemiological data from Brazil, she argued that the pap smear is not the reason for the reduction in cervical cancer mortality in that country.

With the mammogram data, it appears there's a real need to explore what might be changing in mortality related to breast cancer. One point that the authors of the recent study make is that healthcare in general may be improving significantly, such that overall improvements in mortality reflect this shift, independent of the use of mammography screening. Both cervical cancer and breast cancer mortality reductions raise radical paradigm shifts to public health assumptions about screening tools. Perhaps I'm redundant, but I also think this suggests the need for more qualitative data about these practices. Certain tenets are considered almost unassailable in the public health realm. Many subsequent interventions are based on the belief that the pap smear was the way to reduce cervical cancer deaths. When the foundational principles get disrupted, it forces us to examine other related ideas. I think it's a fantastic opportunity.