*4.3. Overtreatment*

The main harm attributed to overdetection of breast cancer is overtreatment. Overtreatment can be considered to be any treatment whatsoever if the cancer is truly overdetected; however, it can also be unnecessarily harsh or aggressive treatment of slowly progressing cancers.

The greatest concerns regarding the overtreatment of breast cancer have been for in situ disease, which is most commonly treated with breast-conserving surgery and radiation therapy. There are now guidelines for acceptable margins (2 mm) for breast conserving surgery that will reduce re-excision rates [34]. For disease that has a low risk of recurring, the possibility of omitting radiotherapy can be considered [35].

However, it is also crucial that in situ disease not be undertreated. In a SEER review of over 144,000 women diagnosed with DCIS, Giannakeas et al. concluded: " ... the risk of dying of breast cancer was increased 3-fold after a diagnosis of DCIS" "(compared to women without a diagnosis of DCIS)" [36].

More recently, it has been shown that a multigene panel based on 12 genes associated with invasive cancer recurrence is predictive of local recurrence after DCIS. Combined with the categorical values of age at diagnosis and tumor diameter, low/medium/high DCIS score can predict a range of 10-year recurrence risks of 6.67 varying from 49% to 7% [37,38]. Further work by the same group in a cohort of 1362 women diagnosed with DCIS in Ontario, Canada, found that the application of the Oncotype DX 21 gene recurrence score was prognostic for invasive local recurrence and risk of breast cancer death [39]. These multigene assays help to predict an individual's risk of recurrence, which can improve treatment recommendations integrating individual-based risk assessment with individual preferences. Further research is underway to identify biomarkers that predict which women with DCIS would and would not benefit from radiation therapy, thereby reducing overtreatment associated with earlier detection of cancer.
