Abstract P2-12-07: Treatment of the breast in occult breast cancer: Results of a prospective Dutch national cohort study with 5 years follow up

Introduction Occult breast cancer (cT0N+M0) is a rare diagnosis and there is insufficient evidence on which to base treatment of the ipsilateral breast. Methods From 2006 till 2008 the Dutch National Cancer Registry identified patients nationwide with possible occult breast cancer. These patients were diagnosed with axillary nodal metastases with no evidence of the primary tumor on physical examination, mammography and ultrasound. Data on histopathology, imaging diagnostics and treatment were collected. After a minimum of 5 years follow up, data on recurrence and survival were gathered and analyzed. Results A group of 71 patients with occult breast cancer was identified. Of these, 7 patients received no local therapy. The remaining 64 patients all underwent surgery with axillary lymph node dissection. Ninety-two percent had MRI of the breast. Three groups were formed: Group A (n=25) had surgery of the breast, group B (n=28) received breast irradiation and group C (n=11) consisted of patients who had no treatment of the breast. Recurrence in the ipsilateral breast was seen in 4 patients (14%) in group B and in 3 patients (30%) in group C. There was 1 local recurrence in group A after breast conserving treatment and no significant differences between groups. After a median of 85 months of follow-up, overall survival (72%, 82% and 82% for group A, B and C, respectively) and distant recurrence rates (12%, 11% and 10% for group A, B and C, respectively) were not significantly different between groups assessed by log-rank test. Conclusion In occult cT0N+M0 breast cancer, conservative treatment of the breast is an acceptable modality which results in similar distant recurrence and overall survival rates. Surgery and breast irradiation appear to reduce the risk of ipsilateral breast recurrence. This is the first prospective study that provides evidence in the current clinical setting to guide treatment for patients with occult breast cancer. Citation Format: de Maat M, Bretveld R, Steevens J, Vissers Y, Hulsewe K. Treatment of the breast in occult breast cancer: Results of a prospective Dutch national cohort study with 5 years follow up. [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 P2-12-07.