Abstract P1-11-03: Rates of ipsilateral breast tumor recurrence (IBTR) following breast concerving surgery (BCS) and hypofractionated radiotherapy for ductal carcinoma in situ (DCIS)

Abstract

Abstract Background: The risk of IBTR following BCS for DCIS is dependent on both tumor and treatment-related factors including surgical margin width and adjuvant therapies. Management strategies should be risk stratified to avoid over/under-treatment with radiotherapy and endocrine therapy. De-escalation of treatments with safe omission of adjuvant therapies may demand a minimum margin of surgical clearance for non-high grade and selected high grade lesions. Methods: A retrospective analysis was undertaken to examine rates of IBTR among patients undergoing BCS for core biopsy-proven DCIS between 1999 and 2010 when a minimum margin width of 5mm prevailed. The local institutional database identified 1260 DCIS cases with or without an invasive component among whom 323 had pure DCIS diagnosed mainly on screening (>90%). A total of 176 patients were treated with BCS alone (27.5%) or combined with breast radiotherapy [15 fractions of 2.67Gy to total dose of 40Gy without boost]. No patients received any form of hormonal therapy (tamoxifen/aromatase inhibitor). Ten patients died from non-breast cancer causes prior to development of IBTR leaving 167 unilateral and 1 bilateral patient (i.e. 168 cases) for analysis with high (72%), intermediate (17.8%) and low (9%) grade DCIS (or ungradeable). Results: At a median follow up of 126 months (range 46 – 180) a total of 14 patients have developed IBTR as a first event (8.33%). Approximately half of these were non-invasive (n= 8) and half invasive (n=6). Half of DCIS recurrences (4/8) occurred in the first 12 months following surgery and all recurrent DCIS cases were manifest by 3 years compared with a steady recurrence of invasive disease up to 10 years of follow up. One case of invasive disease died from subsequent distant metastases with visceral deposits. There was no significant difference in rates of recurrence with (9/121) or without (5/46) irradiation (p=0.534). Among the 14 recurrent cases, 12 had conformal radial margins of 5mm whilst 2 cases had single minimum margins of 3mm and 2mm (accepted without re-excision due to advanced age, co-morbidity or lesion at edge of breast tissue). Characterization of molecular profiles (ER, HER2, Ki-67) for recurrent cases is ongoing. Conclusion: These rates of local control with a target margin of 5mm and selective hypofractionated breast radiotherapy are consistent with published IBTR rates of approximately 1% per annum for DCIS patients treated with BCS and radiotherapy. Routine inclusion of hormonal therapy may be unnecessary for many patients receiving adjuvant radiotherapy with comparable 10 year recurrence rates of 7 - 8% reported in the International Breast Intervention Study (IBIS)-II.""Background: The risk of IBTR following BCS for DCIS is dependent on both tumor and treatment-related factors including surgical margin width and adjuvant therapies. Management strategies should be risk stratified to avoid over/under-treatment with radiotherapy and endocrine therapy. De-escalation of treatments with safe omission of adjuvant therapies may demand a minimum margin of surgical clearance for non-high grade and selected high grade lesions. Methods: A retrospective analysis was undertaken to examine rates of IBTR among patients undergoing BCS for core biopsy-proven DCIS between 1999 and 2010 when a minimum margin width of 5mm prevailed. The local institutional database identified 1260 DCIS cases with or without an invasive component among whom 323 had pure DCIS diagnosed mainly on screening (>90%). A total of 176 patients were treated with BCS alone (27.5%) or combined with breast radiotherapy [15 fractions of 2.67Gy to total dose of 40Gy without boost]. No patients received any form of hormonal therapy (tamoxifen/aromatase inhibitor). Ten patients died from non-breast cancer causes prior to development of IBTR leaving 167 unilateral and 1 bilateral patient (i.e. 168 cases) for analysis with high (72%), intermediate (17.8%) and low (9%) grade DCIS (or ungradeable). Results: At a median follow up of 126 months (range 46 – 180) a total of 14 patients have developed IBTR as a first event (8.33%). Approximately half of these were non-invasive (n= 8) and half invasive (n=6). Half of DCIS recurrences (4/8) occurred in the first 12 months following surgery and all recurrent DCIS cases were manifest by 3 years compared with a steady recurrence of invasive disease up to 10 years of follow up. One case of invasive disease died from subsequent distant metastases with visceral deposits. There was no significant difference in rates of recurrence with (9/121) or without (5/46) irradiation (p=0.534). Among the 14 recurrent cases, 12 had conformal radial margins of 5mm whilst 2 cases had single minimum margins of 3mm and 2mm (accepted without re-excision due to advanced age, co-morbidity or lesion at edge of breast tissue). Characterization of molecular profiles (ER, HER2, Ki-67) for recurrent cases is ongoing. Conclusion: These rates of local control with a target margin of 5mm and selective hypofractionated breast radiotherapy are consistent with published IBTR rates of approximately 1% per annum for DCIS patients treated with BCS and radiotherapy. Routine inclusion of hormonal therapy may be unnecessary for many patients receiving adjuvant radiotherapy with comparable 10 year recurrence rates of 7 - 8% reported in the International Breast Intervention Study (IBIS)-II. Citation Format: Dumitru D, Benson J, Wishart G, Provenzano E. Rates of ipsilateral breast tumor recurrence (IBTR) following breast concerving surgery (BCS) and hypofractionated radiotherapy for ductal carcinoma in situ (DCIS) [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P1-11-03.