Kwon et al. BMC Cancer 2010, 10:557 http://www.biomedcentral.com/1471-2407/10/557 clearly understood, but other literatures also report the similar findings [12,30]. More than half of all patients received breast- conserving surgery in our study, but 31.5% of these patients, mainly T1mic or T1a, did not receive post- operative radiotherapy because the tumor size was extremely small. The local recurrence rate of this group was 3.2% (2 in 62 patients), which was not high com- pared to the patients who received adjuvant radiother- apy (2.9%, 4 in 135 patients). This may have resulted from the very low incidence of recurrence itself; hence, a longer duration of follow up and a larger number of patients are necessary before definitive conclusions can be made regarding the role of post-operative radiother- apy in very small breast cancer. Our study has several limitations. First, recurrence of early breast cancer is known to be discovered not only during the first decade of follow up, but also during the second decade or even later. Therefore, our duration of follow up was not sufficient for an evaluation of breast cancer prognosis regarding the overall survival and long-term recurrence rate, especially in endocrine- responsive disease. However, an analysis of the short- term recurrence rate and risk factors would be valuable for the identification of specific patient groups who require systemic adjuvant chemotherapy after surgery. Second, other important pathological information, such as mitotic activity [31,32] and vascular invasion [33] were not included in this analysis. Third, many patients received systemic adjuvant therapy according to their hormone receptor status and other clinical factors. Therefore, we cannot conclude whether the pattern of recurrence reflects the natural history of specific sub- groups or a response to the adjuvant therapies given. In fact, 92.4% of hormone receptor positive patients received endocrine therapy while 34.5% of hormone receptor negative patients were treated with adjuvant chemotherapy. It is within the realm of possibility that good prognosis of a patients group with positive ER or PR status was caused by the efficacy of the adjuvant hormonal therapy. In addition, ER and PR positivity was defined as 10% or more staining unlike definitions used in recent studies focusing on breast cancer subtypes, which classified tumors as hormone-receptor positive if 1% or more of tumor nuclei were stained [34]. However, we regarded the tumor with 10% or more positive stain- ing as hormone receptor-positive disease, because the pathology report of our patients, especially who were diagnosed in the early 2000s, used the previous classifi- cation standard. There may be a possibility that tumors with positive staining of ER and or PR between 1-9% may have been classified as HR negative. Finally, a definite conclusion pertaining to the sub- group of patients who required systemic adjuvant Page 7 of 8 treatment could not be determined because a multivari- ate analysis could not be performed for predictors of systemic recurrence due to the low number of events. Conclusion We confirmed that patients with a tumor size of 1cm or less of node-negative invasive ductal carcinoma of the breast have excellent short term prognosis. Studies with a larger sample size and a longer follow up duration are needed for confirmation of this result, but patients younger than 35 years of age and triple negative disease were identified to be the highest risk group of recurrence. Acknowledgements Medical Research Collaboration Center in Seoul National University Hospital contributed toward this study by statistic analysis. This study was supported in part by a grant from the Korean Health 21 R&D Project, Ministry of Health & Welfare, Republic of Korea (0412-CR01-0704- 0001). Author details 1Department of Internal Medicine, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea. 2Department of Internal Medicine, Seoul National University College of Medicine, Seoul National University Hospital, Seoul, Korea. 3Department of Pathology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea. 4Department of Radiation Oncology, Seoul National University College of Medicine, Seoul National University Hospital, Seoul, Korea. 5Department of Surgery, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea. 6Department of Radiation Oncology, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seongnam, Korea. 7Department of Pathology, Seoul National University College of Medicine, Seoul National University Hospital, Seoul, Korea. 8Department of Surgery, Seoul National University College of Medicine, Seoul National University Hospital, Seoul, Korea. Authors’ contributions JH Kwon, JH Kim conceived of the study, and participated in its design of the study, coordination, and performed data acquisition, statistical analysis, and interpretation. SYP, EKC, SWK, IAK, TYK, IAP, DYN, YJB and SWH have been involved in revising it critically for important intellectual content. JH Kwon, YJK, KWL, DYO, JH Kim and SAI participated in drafting the manuscript. SAI, TYK, YJB have given final approval of the version to be published. All authors read and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Received: 31 May 2010 Accepted: 15 October 2010 Published: 15 October 2010 References 1. Otto SJ, Fracheboud J, Looman CW, Broeders MJ, Boer R, Hendriks JH, Verbeek AL, de Koning HJ: Initiation of population-based mammography screening in Dutch municipalities and effect on breast-cancer mortality: a systematic review. Lancet 2003, 361(9367):1411-1417. 2. 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