Breast cancer survival and time of mammographic screening

This paper studied the relationship between breast cancer survival in women and the time of mammographic screening.

Mammographic screenings are used to detect breast cancer. However, mammographic screening does not detect all cancers. Between 25-50% of cancers diagnosed in women who undergo screening are cancers that develop between screenings (called interval cancers). Cancers that develop rapidly are more likely to occur as interval cancers than slower developing cancers. Hence, interval cancers are considered to be more aggressive. However, some studies have suggested otherwise. 

Women aged 50-74 years diagnosed with a first breast cancer were examined. Information about the screenings they underwent was obtained. Additionally, prognostic factors (factors that are associated with cancer outcome) like stage (severity of cancer), tumour size, tumour grade (how abnormal cells are under the microscope) and receptor status (presence or absence of hormone receptors) were obtained. Survival rates were calculated.

Of 13,453 cases of invasive breast cancer, there were 1,671 deaths from breast cancer (12.4%). The average 5-year survival rate was 89.9%. Breast cancer detected through screening had the best survival rates. Cancers diagnosed within 12, 12-23 and 24-47 months of a negative screen (no cancer detected) had similar survival rates. Survival was significantly different between cases diagnosed within 48 months and those 48 months after a screen or never screened.

When comparing cancers diagnosed more than 4 years after screening versus those never screened, only cancer stage was a significant prognostic factor. When comparing cancers diagnosed within 4 years of screening to those diagnosed after 4 years or never screened, significant differences were found for size and cancer stage.

The authors concluded that there was no evidence that cancers diagnosed within 12 months had poorer prognosis than those diagnosed up to 48 months following screening. 

The authors worked with a company that manages the mammography screening program.