Abstract P4-16-12: Outcomes of low- risk Ductal Carcinoma in situ in South East Asian women treated with breast conservation surgery.

Abstract

Abstract Background: Singapore is the first South East Asian country to establish a nationwide breast cancer screening programme in 2002. Since then, the incidence of breast cancer and pre-invasive disease, in particular, has increased tremendously. Ductal carcinoma in situ (DCIS) constitutes over a quarter of all screen-detected cancers. In Singapore, most patients with DCIS are managed with breast conserving surgery (BCS). In almost all cases, this is followed by adjuvant radiotherapy (RT) to the whole breast. However, the optimum management of low-risk DCIS remains contentious. Non-randomized data in Caucasian women suggests benefits in the reduction of local recurrence despite already low recurrence rates. Similar information in Asian women is lacking. We examined the outcomes of South East Asian women with low-risk DCIS treated with BCS. Methods: Retrospective chart reviews of patients treated with BCS for DCIS from 1995 to 2011 was performed. Patients meeting the pathological criteria from ECOG 5194 were included: Low-Intermediate grade (LG) DCIS ≥0.3cm but ≤2.5cm excised with final margins ≥3mm and High grade (HG) DCIS ≥3mm but ≤1.0cm. Most patients received adjuvant RT consisting of whole breast RT to 50Gy followed by a 10Gy boost to the tumour bed. Patients deemed to have especially low recurrence risks did not receive RT and some patient declined adjuvant RT. Patients who are oestrogen receptor positive were offered 5 years of tamoxifen. Results: A total of 744 patients with pathological diagnosis of pure DCIS were identified, of which 273 meets the selection criteria: LG (N = 219); HG (N = 54). Median follow-up for these patients is 60 months. Median age at diagnosis is 50 years old. About 70% of patients were screen detected; only 21 of which (7.7%) were diagnosed before the introduction of breast screening. There were 8 ipsilateral breast tumour recurrences (IBTR) in total; 7 of which were DCIS. The estimated actuarial IBTR rates at 5- and 10-year for the entire cohort are 1.8% and 4.3% respectively. In comparison, 10 contralateral new breast primaries were diagnosed in this cohort, giving 5- and 10-year contralateral relapse rates of 1.9% and 7.2% respectively. All patients with LG DCIS received RT except for 9. There were 7 recurrences in this group, two among the 9 patients who did not receive RT. The estimated IBTR rates at 5- and 10-year are 2.3% and 4.2% respectively. All patients with HG DCIS received RT. There was only 1 IBTR occurring beyond 5 years giving an estimated IBTR rate of 4.5% at 10-year. These results compare favourably with the 5-year IBTR rates of 6.1% and 15.3% in the LG and HG patients respectively in the ECOG 5194 study where patients were managed with BCS alone. One patient died of metastatic breast cancer from the contralateral breast giving a 10-year overall survival of 98.5%. Conclusions: South East Asian women with screen detected DCIS have exceedingly low rates of IBTR after breast conservation therapy. The addition of adjuvant RT approximately halved the IBTR rates in our study patients. The high proportion of recurrence in the small group of patients who did not receive RT warns of the potential hazards of managing even these low-risk patients without radiation. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P4-16-12.