Women with a higher body mass index (BMI) are at an increased risk of not detecting their breast tumour until it has become large, according to a new study.
As a result, the researchers said their findings suggested that women with higher BMI may need shorter intervals between mammography screening exams.
“Women with high BMI should consider shorter time intervals between screenings”
The study was carried out in Sweden, which has 18-month to two-year intervals between screenings, and therefore more regular than the current three-year interval for the NHS.
Breast screening is currently offered to women aged 50-70 in England. However, the NHS is in the process of extending the programme as a trial, offering screening to some women aged 47-73.
The researchers noted that, while it was associated with a number of health risks, including diabetes and heart disease, high BMI was not considered as part of breast cancer screening guidelines.
They set out to identify risk factors associated with tumours not being detected until larger than 2cm – about the size of a peanut – and to examine the implications for long-term prognosis.
The 2cm size was important because it was one of the parameters used to separate stage I and stage II cancers, said the researchers from the Karolinska Institutet in Stockholm. In addition, tumour size was known to be strongly associated with prognosis, they highlighted.
The study involved 2,012 cases of invasive breast cancer that appeared from 2001-08, with patients followed until the end of 2015.
For cancers detected at screening, both BMI and breast density were found to be associated with having a large tumour at diagnosis. However, for interval cancers, or cancers detected within two years of a normal mammogram, only BMI was linked with having a large tumour.
Women with higher BMI had worse prognosis than women with lower BMI among interval cancers, noted the study authors, though breast density showed no significant association with progression.
Overweight women may need more frequent mammograms
Study co-author Dr Fredrik Strand said the findings provided more information for clinicians and patients when deciding about optimal screening approaches.
“Our study suggests that when a clinician presents the pros and cons of breast cancer screening to the patient, having high BMI should be an important ‘pro’ argument,” he said.
“In addition, our findings suggest that women with high BMI should consider shorter time intervals between screenings,” said Dr Strand.
He added that, besides the larger interval cancers, women with high BMI may have other factors that put them at risk for a worse prognosis, including the molecular composition of the tumours and hormone receptor expression levels that make them harder to treat.
In future, Dr Strand said he intended to look at how breast density was associated with delayed detection.
The study results are being presented next week in Chicago at the annual meeting of the Radiological Society of North America.