1. Radiological-histological size correlation in triple-negative breast cancer (TNBC) Abstract # 8254 C Thibault 1, M Gosset 2, F Chamming’s 3, M-A Lefrere-Belda 4, N Pécuchet 1, L Fournier 3, H Roussel 4, S Oudard 1,5, F Lecuru 2,5, J Médioni 1,5 BACKGROUND METHODS Preoperative size of breast tumors is a crucial parameter for guiding modality of surgery and neoadjuvant chemotherapy (NAC). Mammography (MG) and breast ultrasound (US) are known to poorly predict tumor size. MRI is considered to be the best imaging but the low specificity limits its use. Few data are available in the TNBC population. We retrospectively collected data on patients treated for a local TNBC in Hôpital Européen Georges Pompidou (HEGP) between 2000 and 2012. To be included, patients had to fulfill the following inclusion criteria: ductal or lobular carcinoma, ER <10%, PR <10% and HER-2 negative. Radiological sizes on MG, US and MRI at initial diagnosis were collected from the medical reports when available. The gold standard was postoperative histological size. We considered that tumor was underestimated when variation size (  S) was  - 3mm, overestimated when  S  + 3mm and adequately estimated when  S was comprised between - 3 and + 3 mm. We calculated the sensitivity and specificity of each imaging technique to identify  pT2 tumors. MG and US tend to underestimate TNBC size without impacting on positivity of resection margin. MG and US poorly predict histological size. These results are consistent with other data reported in general breast cancer population (1,2). MRI better evaluated size in our cohort but the small sample size limits conclusion about the role of MRI in preoperative imaging in TNBC. 1- Fallenberg et al., Eur Radiol 24:256–264, 2014 2- Bosch et al., Eur J Radiol 48:285–292, 2003 3- Mann et al., Eur J Radiol 82:1416–1422, 2013 RESULTS Eighty-five tumors were analyzed (Figure 1). The characteristics of patients are described in table 1. The correlation coefficient between radiological and pathological size was 0.66 for MG (n=40), 0.60 for US (n=60) and 0.74 for MRI (n=10) (Figure 2). MG, US and MRI underestimated tumor size in respectively 58% (n=23/40), 53% (n=32/60) and 10% (n=1/10). MG, US and MRI overestimated tumor size in respectively 10% (n=4/40), 12% (n=7/60) and 50% (n=5/10). MG, US and MRI correctly estimated tumor size in respectively 32% (n=13/40), 35% (n=21/60) and 40% (n=4/10). MG, US and MRI correctly identified  pT2 tumors with a sensitivity and specificity of respectively 65% and 100% (MG), 48% and 92% (US), 100% and 71% (MRI). The frequency of positive resection margin was identical when tumors were underestimated versus  over or correctly  estimated (21% vs 14%, p=0.38). Even when the variation size was increased to - 5 mm, the difference was still not significant (p=0.10). Patients characteristicsPopulation n = 85 tumors MG n=40 US n=60 MRI n=10 Age (median, years)56 (38-88)585647 cT - T0 - T1-T2 - T3-T4 - unknown 3 (4%) 76 (89%) 5 (6%) 1 (1%) 1(2%) 36 (90%) 3 (8%) 0 1 (2%) 54 (90%) 4 (7%) 1 (2%) 1 (10%) 9 (90%) 0 Type of surgery - tumorectomy - mastectomy - unknown 61 (72%) 23 (27%) 1 (1%) 29 (73%) 10 (25%) 1 (2%) 43 (72%) 17 (28%) 0 6 (60%) 4 (40%) 0 Histological type - Ductal invasive carcinoma - Lobular invasive carcinoma - Unknown 82 (96%) 2 (3%) 1 (1%) 39 (98%) 0 1 (2%) 58 (%) 2 (%) 0 (0%) 10 (100%) 0 pT (median, mm)18221812 pN - N+ - N- - Unknown 26 (31%) 58 (68%) 1 (1%) 14 (35%) 25(63%) 1 (2%) 18 (30%) 42 (70%) 0 4 (40%) 6 (60%) 0 Resection margin - negative - positive - unknown 67 (79%) 17 (20%) 1 (1%) 30 (75%) 10 (25%) 0 53 (88%) 7 (12%) 0 7 (70%) 3 (30%) 0 CONCLUSION Table 1: Patients characteristics Figure 2: Correlation between histological size and radiological size REFERENCES Figure 1: Flow-chart n= 107 n= 85 22 excluded (no data available on preoperative imaging) MG n= 40 US n= 60 IRM n= 10 25 excluded 19 missing data 2 calcifications 3 normal US 1 unmeasured mass 45 excluded 15 missing data 10 calcifications 6 normal MG 14 unmeasured mass 75 excluded 74 no MRI 1 unmeasured mass In our retrospective study, radiological tumor size evaluated by MG and US was poorly correlated to histological size. These results are similar to those reported in general breast cancer population (1,2). The only difference is that US usually better estimate tumor size than MG does, which was not observed in our study. This can be explained by the small size of the samples (n=40 for MG and n=60 for US) and by the tumor size which where smaller in US group (22 vs 18 mm). However, the specificity of MG and US to detect  pT2 was good. It allow to consider that MG and US can adequately guide the surgeon to decide to do a tumorectomy instead of mastectomy. As in general breast cancer population (1,3), MRI better evaluated tumor size in our study even if the tumor size was smaller in MRI group than in MG and US groups. But as the tumor size cut-off to do chemotherapy for TNBC is 5 mm, the use of preoperative MRI to decide NAC is limited. However, MRI could be interesting to detect multifocal tumors. In our study, we didn’t analyse the impact of MRI on this parameter because of the small size of the sample (n=10) and because none of the tumors evaluated by MRI was multifocal. DISCUSSION Radiological-histological size correlation in triple-negative breast cancer (TNBC) Abstract # 8254 C Thibault 1, M Gosset 2, F Chamming’s 3, M-A Lefrere-Belda 4, N Pécuchet 1, L Fournier 3, H Roussel 4, S Oudard 1,5 F Lecuru 2,5, J Médioni 1,5 Hôpital Européen Georges Pompidou (HEGP), Assistance Publique hôpitaux de Paris (AP HP), Paris, France 1 medical oncology; 2 gynecologic surgery; 3 radiology department 4 pathology department; 5 Paris Descartes University