To the Editor The recent study by Narod and colleagues1 confirms findings from previous studies that the long-term risk of breast cancer mortality for patients with ductal carcinoma in situ (DCIS) is low. However, breast cancer mortality is not the only relevant end point in optimizing the treatment of DCIS. The development of local recurrence (especially invasive ones) can be psychologically devastating and requires further treatment with surgery and possibly radiation and systemic therapy, which can have a significant detrimental effect on quality of life. Many breast cancer specialists support initial omission of radiation therapy for selected patients with DCIS treated with lumpectomy, provided that patients find the increased risk of local recurrence acceptable.2 Past randomized trials were too small to meaningfully examine the effects of treatment or the outcomes of subgroups defined by prognostic factors on cancer mortality. Narod and colleagues1 found several significant and nonsignificant differences in mortality. However, this study did not include a central pathology review; therefore, the extent to which individuals (especially young women or women with adverse characteristics) had occult invasive cancer at the time of diagnosis is unknown. Their findings would also have greater clinical implications if they examined the effect of alternative therapies on outcomes for specific patient subgroups characterized by either values of individual prognostic factors or common combinations of these. It would therefore be important for the authors to perform a study closely matching individual patients on important risk factors, as well as a propensity score,3(pp165-168) which may help reduce the problem of bias in treatment assignment when analyzing such databases. Such statistical techniques may also overcome problems of interpretation based on Cox regression models when important prognostic variables violate the proportional hazards assumption, as is true for invasive breast cancer4 and possibly DCIS.
Recht A, Rakovitch E, Solin LJ. Treatment and Long-term Risks for Patients With a Diagnosis of Ductal Carcinoma In Situ . JAMA Oncol. 2016;2(3):396. doi:10.1001/jamaoncol.2015.4854