Australian study claims some cancers are better left 'undiscovered'

Breast cancer surgery scar.
Breast cancer surgery scar. Photo credit: Getty

A new study is claiming roughly one in five cancers diagnosed in Australia would be better left untreated.

The study, 'Estimating the magnitude of cancer overdiagnosis in Australia', was published in the Medical Journal of Australia on Monday. 

The research estimates 42 percent of prostate cancers, 42 percent of renal cancers, 73 percent of thyroid cancers, 58 percent of melanomas and 22 percent of invasive melanomas in men are overdiagnosed - or 24 percent of all cancer diagnoses.

For women, an estimated 22 percent of breast cancers (invasive cancers, 13 percent), 58 percent of renal cancers, 73 percent of thyroid cancers and 54 percent of melanomas (invasive melanoma, 15 percent) were overdiagnosed - or 18 percent of all cancer diagnoses.

After analysing changes in "absolute lifetime risks for prostate, breast, renal, thyroid cancers and melanoma between 1982 and 2012", the report concludes that 11,000 cancers in women and 18,000 cancers in men are estimated to be "overdiagnosed" annually in Australia. 

The study argues that cancer checks can often reveal more harmless or benign cancers, leading to intensive treatments, surgery and chemotherapy which come with their own sets of health hazards.

Australia's Cancer Council CEO, Professor Sanchia Aranda, told the Sydney Morning Herald that not always knowing which cancers are overdiagnosed - and which pose a threat - is a significant issue.

"Not diagnosing a cancer and having a woman die would be considered a bigger harm than the damage of getting a cancer diagnosis of a cancer that might not have harmed you," Aranda said.

The researchers compared cancer rates between 1982 and 2012, a period in which Australia's cancer incidence rate rose by roughly 30 percent while the rate of fatalities fell.

It's noted that breast cancer screening can be particularly difficult, with doctors frequently being unable to tell if the cancer is harmless or life-threatening - hence, breast cancers are predominantly treated with surgery or chemotherapy. 

Professor Alexandra Barratt, one of the study's authors and a University of Sydney breast cancer screening researcher, told the outlet that she struggles with the risks of screening. 

"There are potential benefits and potential harms and I am very concerned about the risk of being overdiagnosed and overtreated," she said.

Prostate cancer is also overdiagnosed, with the Royal Australian College of GPs now recommending against prostate cancer screening.

The team suggests further research to develop improved cancer tests and increased information regarding the pros and cons of cancer screening. 

A campaign in the UK provides women undergoing mammograms with a leaflet explaining that for every 200 women screened, three will undergo unnecessary surgery for a cancer that would have never caused symptoms. One will have her life saved.