Bottom Line: In a retrospective study, the 313-SNP breast cancer polygenic risk score (PRS313) blood test could predict future incidents of breast cancer in women diagnosed with ductal carcinoma in situ (DCIS) or lobular carcinoma in situ (LCIS).
Journal in Which the Study was Published: Cancer Epidemiology, Biomarker & Prevention, a journal of the American Association for Cancer Research (AACR)
Author: Jasmine Timbres , clinical information analyst at King's College London and the study's lead author, and Elinor J. Sawyer, PhD , the study's senior author and professor of clinical oncology at King's College London in the United Kingdom.
Background: Breast cancer is the most common form of cancer in women and contributes to more than 15% of all new cancer cases in the United States. Abnormal cells in the breast ducts (DCIS) and breast lobules (LCIS) can develop into breast cancer, but scientists cannot currently predict which DCIS and LCIS cases will go on to become breast cancer, said Sawyer. "It is therefore very important that we find ways to predict which women with DCIS and LCIS are most likely to develop invasive breast cancer in the future so they can be given the most appropriate treatment and avoid unnecessary treatment," she said.
Timbres wanted to test whether PRS313 could be a useful tool in filling this gap in risk assessment and guiding treatment. PRS313 is a test that estimates a patient's breast cancer risk by quantifying which of 313 breast cancer-associated gene abnormalities called SNPs they have. Because PRS313 has been previously validated as a genetic test that can predict the risk of breast cancer in women with no cancer history, Timbres hypothesized that it could be used as a prediction factor for the risk of breast cancer in patients with DCIS or LCIS.
How the Study was Conducted: To test the predictive power of PRS313 in DCIS and LCIS patients, the researchers analyzed the datasets from the U.K. ICICLE and GLACIER studies. The team assessed the PRS313 scores and follow-up data from 2,169 DCIS cases and 185 LCIS cases. For patients with DCIS, the researchers stratified the PRS313 scores into quartiles and compared them with outcomes. For patients with LCIS, they measured associations between increasing PRS313 scores and outcomes.
Results: The study found that, among patients with DCIS, those with PRS313 scores in the highest quartile were 2.03 times as likely to develop cancer in the breast opposite the original breast (i.e., the contralateral breast) compared with patients in the lowest PRS313 quartile. However, the association between a higher PRS313 and future same-breast (ipsilateral) cancer in patients with DCIS was not significant.
In patients with LCIS, an increasing PRS313 score was associated with an increased risk of ipsilateral breast cancer, being 2.16 times more likely to develop ipsilateral disease per increase in PRS313.
Family cancer history also appeared to play a role. The researchers found that, in patients with a family history of breast cancer, increases in PRS313 were associated with a more than threefold increase in the risk of ipsilateral disease after LCIS, and the risk increased to fourfold if patients who had received mastectomy and radiotherapy for their cancer were excluded.
Author's Comments: "LCIS is not always surgically removed or treated with hormone therapies, as it is considered lower risk than DCIS. However, these results indicate that those with a family history may benefit from such additional treatments, which could reduce their risk of further cancer," Timbres said.
"The associations found in this study could be useful in helping women decide their treatment options after a diagnosis of DCIS or LCIS," she added. "By looking at the full picture, rather than just how cells look under a microscope, we can give women more accurate information about their personal risk of recurrence. This could help them make more informed choices about their treatment options and what's right for them."
Sawyer noted, "Although more work still needs to be done to confirm the results of this study in other groups of patients or assess additional genetic changes, the results are very promising and have the potential to influence treatment decisions."
Study Limitations: The study's limitations include PRS313's design as a risk score for invasive disease specifically, and the study therefore may not have tested for important but as-yet-unknown genetic changes associated with in situ breast disease. Another limitation is that the number of women with LCIS in the study's cohorts was quite small, which may have led to the researchers not detecting statistically significant associations.
Funding & Disclosures: The study was funded by Breast Cancer Now, Cancer Research UK, and the Biomedical Research Centre at Guy's and St Thomas' NHS Foundation Trust and King's College London. Timbres and Sawyer report no conflicts of interest.
