Abstract P2-12-14: Therapeutic mammoplasty reduces high incomplete excision rate in lobular cancer

Abstract

Abstract Introduction: Incomplete excision rate for lobular cancer is much higher compared to other types of breast cancer, since lobular cancer is frequently occult on imaging. This, and the inability to downstage lobular cancer with neoadjuvant therapy lead to the highest mastectomy rate of all subtypes. Here, we investigated the association between histopathological characteristics and incomplete excision as well as mastectomy rates. Further, we investigated whether the application of level 2 therapeutic mammoplasty (TM) would extend the indication for conservation with lobular cancers. Methods: Data of 1389 consecutive patients underwent surgery for (non)invasive breast cancer between January 2008 and June 2012 was analysed. Pathological and preoperative radiological results were analysed in the context of final surgery and tumour excision margins. Statistical significance was calculated using Chi-square, Mann-Whitney and Z-tests with a significance<0.05. Results: Overall incomplete excision rate was 13.74% (131/953), and mastectomy rate was 35.35% (491/1389). Higher incomplete excision and mastectomy rates were strongly associated with lobular subtype (IE: 26.03% (19/73)); M: 51.22% (63/123); p<0.01 vs. other subtypes), node positivity (IE: 25% (36/144) vs. 10.43% (68/652); p=0 and M: 60.69% (193/318) vs. 25.65% (216/842); p=0) and tumour size (IE:T3 80% (4/5) vs. T2 22.51% (43/191) vs. T1 9.23% (55/596); all p<0.01; and M: T3 95.35% (41/43) vs. 59.46% (242/407) vs. 16.16% (112/693); all p=0). Incomplete excision rates were independent of hormonal and HER-2 expressions (ER+: 12.55% (89/709) vs. ER-: 16.67% (15/90); p=0.27 and HER2 neg.: 12.67% (91/718) vs. HER2 pos.: 16.67% (13/78); p=0.32) and it was just higher in grade 2 and 3 cancers (14.6% (60/411); p=0.037 and 16.22% (36/222); p=0.021 vs. G1:6.86% (7/102). However, hormonal and HER-2 expressions as well as tumour grade were in strong association with mastectomy rate (ER pos.: 33.28% (335/1007) vs. ER neg.: 48.75% (78/160); p<0.01; HER2 neg.: 33.43% (341/1020) vs. HER2 pos.: 49.65% (71/143); p<0.01; G3: 50.49% (205/406) vs. G2: 30.77%(172/559) vs. G1: 14.28% (17/119); all p=0). 135 patients underwent surgery for lobular cancer (simple wide excision: 66; TM:19; mastectomy: 50). TM was offered for significantly larger tumours than lumpectomy (28.29mm (10-62) vs. 19.96mm(5-57);p<0.01; vs. mastectomy: 37.56 mm(5-110);p=0.096). Incomplete margins were found with significantly smaller tumours when lumpectomy was applied compared to TM(25.94 mm(6-56) vs. 38.6 mm(30-45);p=0.031). Conservation was achieved with significantly bigger tumours when TM was used (25.46mm (10-62) vs. 17.66mm (5-57); p=0.032). Multifocality, however, significantly increased the chance for incomplete excision even after TM (4/7; p=0.019). Conclusion: Higher incomplete excision rate is strongly associated with lobular subtype, node positivity and tumour size, but independent of hormonal end HER-2 expression, while tumour grade is not a strong predictor. All histopathological characteristics are strong predictors of final mastectomy rate. Using TM, breast conservation can be achieved for significantly larger lobular cancers, and incomplete excision rate decreased in smaller cancers, which are routinely treated with wide excision. Citation Format: Romics L, Kabir SA, Mansell J, Mallon EA, Stallard S, Doughty JC. Therapeutic mammoplasty reduces high incomplete excision rate in lobular cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-12-14.