Medical history is dotted with stories of cancers vanishing without a trace and without any treatment, either.  Once considered medical oddities, a new study suggests more cancers go away without treatment than would be expected.  The theory, however, is quite difficult to prove conclusively because almost every cancer detected is treated aggressively, leaving no opportunity to explore spontaneous regressions.

Leading the study were Dr. Jan Maehlen, of the Ulleval University Hospital, Oslo, Norway; Dr. H. Gilbert Welch, of the Dartmouth Medical School in Vermont; and Dr. Per-Henrik Zahl, of Norway’s Institute of Public Health.  The research team compared mammogram records of women, all between 50 and 64 years old, for the six-year period from 1992 till 1997 and from 1996 till 2001.  Norway first started using mammography in 1996.

All the 109,784 women in the earlier study period were offered mammograms in 1996 and 1997 and almost all of them accepted the offer as did almost all the 119,472 women in the later group.

While the researchers expected to find a similar prevalence of breast cancer in both groups of women, they were surprised to find the later group had 22% more cancers (1,909 cases of invasive breast cancer) than the earlier group (1,564 cases).

The research group suggests other explanations for the cancer rate discrepancy but none is more likely than the possibility that the women in the earlier group, without access to mammography, actually developed cancer at a rate similar to the women of the later group but, without detection, many of these cancers disappeared of their own accord, before they were ever detected.

The study’s findings do not implicate mammograms as a cause for the later group’s higher incidence of cancer nor does it suggest women should forego mammogram screenings.  There is no doubt mammograms save lives but undisputed knowledge about how cancer progresses is in short supply, making it impossible at this time to determine which cancers require medical intervention and which do not.

The research team describes their study’s design as not perfect but establishing a perfectly designed study of this nature is unrealistic.  To conduct such a study, some women with breast cancer would need to be treated while others would be required to refrain from treatment.

Some alternative explanations for the striking difference in cancer rates between the two groups include:

• Postmenopausal women who use hormone-replacement therapies (HRT) are more likely to be screened for breast cancer than those who do not but this possibility accounts for less than 3% of the outcome.
• Improved mammography technologies emerging during the later study period but the sensitivity rate of the technology remained relatively stable throughout the study period.
• The later group of women may have had a higher likelihood of developing cancer but cancer risk factors were thought to be strikingly similar in both groups of women.
• Women in the first group, when mammography was new to Norway, received only one screening while the later group had mammography available for repeated screenings over the course of the study.  Analysis, however, revealed no increased likelihood of detection with repeated screenings.

Medical science has documented similar spontaneous regressions of cancer but Dr. Barnett Kramer, director of the National Institutes of Health’s Office of Disease Prevention, says the frequency of such events, as suggested by the Norwegian study, is “shocking.”  Speaking with the understanding that the research does not completely rule out other possibilities, he says the research indicates other explanations are not very likely.

The study has piqued the interest of Dr. Robert M. Kaplan, who is interested in replicating the study.  Saying the “implications are potentially enormous,” Kaplan, who serves as department chairman of health services at the University of California, Los Angeles, School of Public Health, is considering a similar study based in Mexico, where mammography screenings are just now becoming available.

The chairman of Houston’s MD Anderson Cancer Center, Donald A. Berry, expressed concerns about the ability of screening tests to detect cancers at an increasingly early rate.  He fears such early detection, and the aggressive treatment that follows such a diagnosis, may be causing people to treat cancers that might otherwise go away on their own.  He would like to see more study done on the natural history of cancer with the hope of learning which cancers are dangerous, requiring treatment, and which are not.

Dr. Laura Esserman, surgery and radiology professor at the University of California in San Francisco, looks forward to the day she can tell her patients not to worry because their cancer isn’t real and will go away on its own.

A report of the study has been published in the November 25 issue of the ‘Archives of Internal Medicine.’

Source: NYT