Grant: Project Grant

Ductal carcinoma in situ (DCIS) is a non-invasive breast cancer that represents over 25% of all new breast cancers in North America. Treatment is recommended given the potential of DCIS to progress to invasive cancer. Most women are treated with breast-conserving surgery followed by breast radiation which can lower the risk of breast cancer recurring. Breast radiotherapy carries a risk of toxicity and has no impact on survival. Therefore, there is great interest to reduce over-treatment by identifying the subgroup of individuals with DCIS who have a very low risk of recurrence after local excision for whom it is safe to omit radiation. Currently, clinicians use clinical and pathological criteria to estimate an individual's risk of local recurrence after breast-conserving surgery such as age at diagnosis older than 45 years, tumor size 2.5 cm or less, low/intermediate grade and clear margins, but these features at best identify women whose risk of local recurrence 10 years after breast-conserving surgery is 11-15%. Given that most women with DCIS receive radiation suggests that this risk is considered too high to omit radiation. The Oncotype DCIS Score is the first genomic test for DCIS. Integration of the DCIS Score with clinicopathological features can more accurately estimate local recurrence risks after surgery and may help identify a subgroup of women with a lower risk of recurrence where there would be greater consensus and patient satisfaction to omit radiotherapy. We propose a national prospective cohort study validating that the revised DCIS Score can identify a group of women at very low risk of recurrence following local excision. We will include 500 women older than 45 years, with tumour size <2.5cm, clear margins, low/intermediate grade and Oncotype DCIS score <39, who have an estimated 10-year risk of local recurrence <10%. Prospective validation is necessary to change clinical practice, personalize treatment and reduce over-treatment of DCIS.