A prognostic score based on tumor size, age, and nuclear grade indicated the magnitude of survival benefit from radiation therapy (RT) after breast-conserving surgery for ductal carcinoma in situ (DCIS).
For patients of younger age with larger tumors and higher nuclear grade, survival among those who received radiation therapy was significantly better than among those who did not. In the absence of these risk factors, survival was similar for the RT and non-RT groups. The magnitude of the survival improvement with RT was significantly correlated with the patient prognostic score: for score 0, hazard ratio (HR) was 1.2 (95% CI, 0.67 to 2.06); for score 5, HR was 0.29 (95% CI, 0.09 to 0.91).
“Overall [breast cancer mortality] was only approximately 1%, whereas mortality from other causes was approximately 10% in our study. These results, when taken together with our earlier findings on DCIS, suggest that further research investigating the overdiagnosis and overtreatment of breast cancer is warranted and that a less invasive and more individualized local treatment strategy on the basis of one’s probability of local recurrence should be considered,” wrote Dr. Yasuaki Sagara of Brigham and Women’s Hospital and Dana-Farber/Brigham and Women’s Cancer Center, Boston, and colleagues (J Clin Oncol. 2016 Feb 1. doi: 10.1200/JCO.2015.65.1869).
The retrospective longitudinal cohort study used SEER data of 32,144 patients with DCIS: 20,329 (63.2%) received radiation therapy and 11,815 (36.8%) did not. At a median 8-year follow up, there were 304 breast-cancer specific deaths (0.9%).
The patient prognostic score is based on three factors: age, tumor size, and histology, with a cumulative score ranging from 0 (lowest risk) to 6 (highest risk). Patient age categories are 61 years or greater (0 points), 40-60 years (1 point), and 40 years or less (2 points); size categories are less than 16 mm (0), 16 mm to 40 mm (1), and 41 mm or greater (2); histology categories are low grade (0), intermediate grade (1), and high grade (2).
Investigators cautioned that this retrospective study was unable to measure potential confounders, such as surgical margin status, endocrine therapy, patient comorbidities, and reasons for treatment selection, which are factors that can significantly impact overall survival outcome measures.
The researchers highlighted the utility of the prognostic score in predicting survival benefit of RT, which can guide individual treatment decisions.
“As an oncology community, we must be cognizant of overtreatment for this disease process that has low [breast cancer mortality],” they wrote.