Breast induration and irradiated volume in the DBCG HYPO trial: The impact of age, smoking, and boost

Purpose
To investigate the association between irradiated breast volume and grade 2–3 breast induration three years after radiotherapy in the phase III Danish Breast Cancer Group HYPO trial randomizing patients ≥ 41 years to whole breast irradiation (WBI) with 40 Gy/15fr versus 50 Gy/25fr.

Methods
Treatment plans were available for all Danish patients. Associations between frequency of induration and irradiated volume, age, smoking status, and boost were assessed by logistic regression. A sequential boost was given to patients < 50 years or in case of a narrow (<2 mm) resection margin.

Results
RT plans from 1,333 patients were analyzed with 178 (13 %) having grade 2–3 induration. 1135 patients had only WBI. For this group, induration was correlated with irradiated breast volume for patients ≥ 65 years (n = 343, 10 %/22 % for small/large irradiated volumes, p = 0.005) but not for patients aged 50–64 years (n = 792, 11 % for both small and large volumes, p = 0.82). Smoking doubled the frequency irrespective of irradiated volume and age. All patients < 50 years (n = 156) had a boost. A volume effect was found for this group (5 %/21 % induration for small/large volume, p = 0.002). 42 patients ≥ 50 years had a boost and 14 (33 %) had grade 2–3 induration, however, with a p-value > 0.05 due to the few numbers of patients.

Conclusion
A relationship between irradiated breast volume and 3-year frequency of breast induration was found for patients ≥ 65 years, whilst not for patients aged 50–64 years. Smoking doubled the risk of induration irrespective of volume and age. A dose-induration relationship was seen for boost patients < 50 years.