Researchers from Karolinska Institutet have shown in a new study that so called interval cancer, which is detected between two screening sessions, constitutes a significant proportion of breast cancer cases and that certain risk factors can increase the likelihood of developing this type of cancer. The study was published in the journal JAMA Oncology.

Mammography screening has been shown to be effective in reducing breast cancer mortality by detecting cancer at an early stage. However, some cancers are not diagnosed during screening but between two screening rounds, known as interval cancer. This form of cancer can be more aggressive and difficult to treat than breast cancer detected during a scheduled screening. 

The study, which includes half a million women in Stockholm between 1989 and 2020, shows that interval cancer constitutes a significant proportion of all breast cancer cases. 

Yuqi Zhang
Yuqi Zhang. Photo: Mujin Ye
We could see that interval cancers make up about 30 percent of all breast cancer cases detected during screening, and this percentage has remained constant over three decades, despite advances in screening technology, says Yuqi Zhang , postdoctoral fellow at the Department of Medical Epidemiology and Biostatistics , Karolinska Institutet and the study's first author. 

The researchers identified several factors that increase the risk of developing interval cancer. These factors include high breast density, hormone therapy, higher education level, and older age at first birth. 

Women with high breast density and use of hormone therapy are at increased risk of being missed during screening due to false negative results, says Yuqi Zhang. 

Rapid growth of tumor
Additionally, the study showed that women with a family history of breast cancer, especially interval cancer, are at a higher risk of developing interval cancer themselves. Women with a family history of breast cancer were 1.9 times more likely to develop interval cancer, and this risk increased to 2.9 times if they had a family history of interval cancer specifically. 

This is often due to the rapid growth of tumors between screening rounds rather than missed detections. The study therefore highlights the need for more frequent or improved screening methods specifically designed for women with these particular risk factors, says Yuqi Zhang. 

The study was funded by, among others, the Swedish Research Council and the Swedish Cancer Society. There are no reported conflicts of interest.

Source : https://nyheter.ki.se/tre-av-tio-brostcancerfall-upptacks-mellan-screeningtillfallen