New Delhi: A study in the US has estimated that breast cancer is overdiagnosed in about one in every seven women — aged between 50 to 74 years — who undergo a mammogram in the country.
Overdiagnosis means a detection and diagnosis of breast cancer that would not have progressed to symptomatic cancer during the woman’s lifetime. Many interpret it to mean that the diagnosis would not have caused harm during a woman’s lifetime.
The study by researchers from Duke University Medical Center and Department of Mathematics, published in the journal Annals of Internal Medicine last week, said many of the diagnoses were pre-cancers that may not have grown into full blown malignancy, and the women may have died of other causes. Some others were progressive cancers in older women, where again other causes may have proved fatal, even before the cancer did, the study found.
“On the basis of an authoritative US population data set, the analysis projected that among biennially screened women aged 50 to 74 years, about 1 in 7 cases of screen-detected cancer is overdiagnosed. This information clarifies the risk for breast cancer overdiagnosis in contemporary screening practice and should facilitate shared and informed decision making about mammography screening,” the study stated.
The study cohort included 35,986 women, 82,677 mammograms, and 718 breast cancer diagnoses. “In a program of biennial screening from age 50 to 74 years, 15.4 per cent of screen-detected cancer cases were estimated to be overdiagnosed, with 6.1 per cent due to detecting indolent preclinical cancer and 9.3 per cent due to detecting progressive preclinical cancer in women who would have died of an unrelated cause before clinical diagnosis,” the researchers wrote.
According to some estimates, it is feared one in eight women in the US (about 13 per cent) will develop invasive breast cancer over the course of her lifetime.
Breast cancer screening guidelines given by different US organisations vary. While the US Preventive Services Task Force and American College of Physicians recommend that women in the 50-74 years age bracket, whose risk profile is “average”, should undergo a mammography once every two years, others, including the American College of Radiology and the American Cancer Society, recommend annual screening.
Relevance for India
Breast cancer is the most common form of cancer in Indian women, but regular screening is usually limited to the urban centres.
The ICMR-National Centre for Disease Informatics & Research National Cancer Registry Programme, according to a 2020 estimate, put breast and cervical cancers among the top two cancers affecting Indian women. Breast cancers are estimated to contribute 2.0 lakh (14.8 per cent) and cervical cancer are estimated to contribute 0.75 lakh (5.4 per cent) of all cancers in women.
In India, women with average risk profile are recommended to have their first mammography at 40 years. Those with genetic mutations predisposed to breast cancer or history of cancer in the family need to start at 25-30 years.
In 2010 the National Programme for Prevention and Control of Cancer, Diabetes, Cardiovascular Diseases and Stroke (NPCDCS) was launched. However screening for cancer took off only around 2016- 2017, and halted during the Covid-19 pandemic.
(Edited by Poulomi Banerjee)