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In a previous study (ESTRO Turin 2018), we evaluated the influence of regional nodal irradiation axillary level I-IV vs level III-IV on long term toxicity of the OARS in patients with breast cancer, SNB positive to either 1 or 2 nodes and SNB alone or ALND.  We reported that modality of primary axillary treatment in these patients did not influence the dosimetry of the risk organs except for mean dose thyroid and average contralateral breast. That showed: Dmean thyroid: 24.35±13.04 in group SNB vs 16.43±7.95 in ALND, p=0.007. Dmean contralateral breast: 2.292±1.31 vs 2.08±1.57, p=0.03. In the multivariate analysis, only radiation therapy modality and maximal radiation dose were significantly associated with this parameter. The aim of the present study was to evaluate long term toxicity of these OARS, specially focusing on thyroid function and the presence of radiation-induced second tumors. 

Between October 2012 to September 2017, 63 women with cT1-T2 cN0 breast cancer that after pathological staging were pN1 (only 1 or 2 affected nodes), were treated by adjuvant radiotherapy. They were allocated into two groups: 26 (41.6%) of them were staged by SNB and irradiated axillary levels I-IV and 37 (58.7%) were staged by ALND only levels III-IV were irradiated. We followed up these patients until September 2021.  Age, histology, laterality, cTNM, pTNM, stages and immunohistochemistry, were similar in both groups (Table I). We also recorded TSH, thyroid hormones and the presence of radiation-induced second tumors. Comparisons were done by using chi squared, Student’s t test.  Multiple lineal regression was used when several variables showed significance in the univariate analysis. Significance level was set at 95% (p < 0.05).

Time of follow up was 72,72±21,23 months. Breast late toxicity accordingly to both medical and patient criteria, was similar in both groups 7,4% Vs. 16,7% p =0.44, All cases of lymphedema (n = 6) were present in the group ALND (0% vs. 16,7%; p=0.03). There were slightly more cases of abnormal thyroid function in women with SNB than in patients with ALND 23,8% Vs. 5,9%, p = 0.09. There were more cases of history of thyroid disease in this group (18,5% Vs. 2,8%), p = 0.07. Dmean thyroid was similar in patient with and without history of thyroid disease (19,7±11,35 Vs. 19,56 ± 3,41) (p = 0,98). Thyroid mean dose was also similar in women with and without further thyroid function abnormality (21,23±2,55 Vs 18,32±9,98; (p=0,14). There were no cases of second breast cancer on the contralateral breast. There were only two deaths due to lung metastases. The rate of breast-cancer specific survival was 96,8%. There were no differences in the rate of radiation-induced second tumors 7,4% Vs. 8,3%) p=0,99. 

The majority of patients survived after 6 years. The differences in Dmean thyroid did not influence in thyroid function. The increased Dmean contralateral breast, was not associated with radiation-induced second tumors on this location.