Annelotte van Bommel

122 completed education, stage of disease (clinical), multifocality, unilateral or bilateral mastectomy, axillary dissection, neo-adjuvant chemotherapy, radiotherapy, and IBR hospital volume. Variables were selected based on our previous research 13,17 and literature on factors affecting the use of IBR. 32 All statistical analyses were performed using STATA (STATA Version 14). 33 RESULTS Respondents Five hundred and two patients with IBR and 716 without IBR received an invitation. Two hundred and fifty-three patients who had received IBR and 305 patients without IBR responded, giving a total of 558 responses (46%). Twenty-four patients were excluded due to incomplete questionnaires, leading to valid data from 534 patients (n=229 IBR, n=305 without IBR). Twenty-four patients who reported they had had DBR were excluded for the analyses, leaving 281 patients without IBR. No statistically significant differences between respondents and non-respondent groups were found in baseline characteristics (tumor morphology, year of surgery, IBR hospital volume) other than that respondents were younger than non- respondents (p<0.001). The respondent group consisted of relativelymore patients who had received IBR compared to the non-respondent group (p=0.027; data not shown). Respondents with IBR compared to respondents without IBR significantly differed in patient (age, education, socioeconomic status, comorbidities, BMI), tumor (stage, grade, lymph node status, multifocality), and treatment characteristics (unilateral or bilateral (prophylactic) mastectomy, radiotherapy), as well as hospital factors (IBR hospital volume, hospital type; all p-values<0.05). Both groups were equally treated with chemo-therapy (46% vs 51%, p=0.301) and equally received neo-adjuvant treatment (11% vs 17%, borderline significance: p=0.085; Table 1 ). The majority of patients with IBR either had received a tissue expander followed by a definite implant (55%) or adirect-to-implant (32%) reconstruction; other reconstruction types were latissimus dorsi flap (4%), DIEP flap (5%), or Superior Gluteal Artery Perforator (SGAP) flap (1%; 3%unknown; data not shown in Table 1 ).