Breast cancer may spontaneously regress if left alone, researchers suspect. They have found that even advanced, aggressive breast tumours have disappeared after six years or so without any treatment or medical intervention.
The research team made the discovery by accident while they were researching the effects of regular mammogram screening.
Mammogram screening is recommended in most countries and especially for women aged 50 and above. Numbers of cases of breast cancer have also increased with the introduction of screening programmes, but doctors have assumed this is simply because screening is detecting more cases.
But researchers from the Veterans Affairs Medical Center in Vermont uncovered a different story when they assessed the benefits of a screening programme for women living in four counties in Norway. The country introduced biennial screening in 1996.
They took two groups of women with similar backgrounds and profiles, and all aged between 50 and 64. One group had three mammograms between 1996 and 2001, while the controls had just one mammogram after the six years.
The cumulative rate of breast cancer was far higher in the screened group, as would be expected. But the researchers were puzzled when the controls had their one-time mammogram six years later, as in many cases the cancer that had been detected at the beginning of the study had gone. Overall, the cancer rate was 22 per cent higher in the women who were regularly screened.
As the researchers point out, medical ethics doesn't allow cancer to follow its natural path without intervention and so there is very little evidence of this phenomenon. Nonetheless, there are many individual cases of cancers that naturally regress, and this is recognised as a possible outcome of cases of metastatic melanoma and metastatic renal cell carcinoma in particular.
(Source: Archives of Internal Medicine, 2008; 168: 2311-2316).