Kwon et al. BMC Cancer 2010, 10:557 http://www.biomedcentral.com/1471-2407/10/557 were diagnosed at the Seoul National University Hospi- tal and Seoul National University Bundang Hospital using the hospital cancer registry. Among these, we excluded 2907 patients (74.7%) with more advanced stage cancer than T1bN0, 76 patients (1.9%) who received neoadjuvant chemotherapy, and 81 patients (2.1%) with recurrent breast cancer. Rest of the patients (n = 450, 11.6%) received diagnosis but did not undergo operation in our hospital therefore were excluded from the study. A total of 375 (9.6%) women were eligible, and 120 patients were classified as T1mic, 93 as T1a, and 162 as T1b. Median age was 49 years (range, 24 to 77 years), and 23 patients (6.1%) were under 35. The majority of the study population (182 patients, 48.5%) was asymptomatic at the time of diagnosis, and these patients were diagnosed by screening mammography. Isolated microcalcification was the most common mam- mographic finding (149 patients, 40.9%). Pathologic information including hormone receptor and HER2 sta- tus was available in 99% of patients. Twenty six percent of patients had HER2 positive tumors, defined by 3+ staining on immunohistochemistry; 67.3% had hormone receptor positive disease; and 15.1% had triple negative disease. Table 1 shows the baseline characteristics of the three T stage sub-groups. The age distribution between each patient T stage group was similar. In the microinvasive (T1mic) group, there were significantly higher percen- tages of negative ER and negative PR disease compared to the T1a and T1b groups (57.6% vs. 34.4%, 22.2% for ER, 68.6% vs. 48.4%, 37.7% for PR; p < 0.0001). T1mic tumor also had a higher proportion of HER2 positivity (p < 0.0001); 54 patients (45.8%) in the T1mic group, 21 (22.8%) in T1a, and 21 (13.0%) in T1b. The frequency of positive immunohistochemical staining for p53 was also highest in the T1mic group (p = 0.080 by chi-square, p = 0.037 by Linear-by-Linear association). Ki-67 did not show significant differences between each patient group. Among the 255 patients with T1a or T1b tumor, data of associated DCIS was available in 248 patients. One-hundred and ninety-eight (79.8%) had associated DCIS around the invasive portion, 79 (88.8%) in T1a and 119 (73.6%) in T1b. Loco-regional and adjuvant treatment 178 patients (47.5%) received a mastectomy, and breast- conserving surgery was performed in 197 women (52.5%). For axillary lymph node examinations, more patients (255 patients, 68%) received axillary lymph node dissection than sentinel lymph node biopsies. Among patients who received breast-conserving surgery, 135 patients (68.5%) were treated with adjuvant radio- therapy after surgical resection. The proportion of patients receiving adjuvant whole breast radiotherapy Table 1 Baseline characteristics of all patients according to T stage All T1mic T1a T1b patients (N = 375) (N = 120) (N = 93) (N = 162) Page 3 of 8 P value 0.297 0.126 50 24 - 73 20(12.3) 103(63.6) 39(24.1) 36(22.2) <0.001 126(77.8) 61(37.7) <0.001 101(62.3) 141(87.0) <0.001 21(13.0) 122(75.3) <0.001 11(6.8) 10(6.2) 19(11.7) 104(65.0) 0.080 56(35.0) 121(75.6) 0.223 39(24.4) Age at diagnosis Median Range Grade¶ 1 2 3 ERa PRb Negative Positive Negative Positive HER2c Negative Positive HR/HER2 HR+HER2- HR+HER2+ HR-HER2+ HR-HER2- p53d <10% ≥10% Ki-67d <10% ≥10% 49 24 - 77 28(11.2) 152(60.6) 71(28.3) 136(36.5) 237(63.5) 187(50.1) 186(49.9) 276(74.2) 96(25.8) 220(59.1) 31(8.3) 65(17.5) 56(15.1) 220(60.6) 143(39.4) 275(75.8) 88(24.2) 49 27 - 74 . . . 68(57.6) 50(42.4) 81(68.6) 37(31.4) 64(54.2) 54(45.8) 42(35.6) 11(9.3) 43(36.4) 22(18.6) 60(52.2) 55(47.8) 82(71.3) 33(28.7) 47 29 - 77 8(9.0) 49(55.0) 32(36.0) 32(34.4) 61(65.6) 45(48.4) 48(51.6) 71(77.2) 21(22.8) 56(60.9) 9(9.8) 12(13) 15(16.3) 56(63.6) 32(36.4) 72(81.8) 16(18.2) ¶ Nuclear/histologic grade was assessed only in T1a and T1b patients. a,bData of hormone receptor status was available in 373 patients. ;<10%; negative, ≥10%;positive. c HER2 status was determined by immunohistochemistry and was available in 372 patients.; 0,1+,2+;negative, 3+;positive. dData of p53 and Ki-67 was available in 363 patients. was different in each T stage group: 30 (56.6%) in T1mic, 30 (63.8%) in T1a, and 75 (77.3%) in T1b (p = 0.007). 278 patients (74.1%) received systemic adjuvant ther- apy. Among patients with hormone-receptor positive disease, 232 (92.4%) received adjuvant endocrine ther- apy. No differences were observed in the percentage of patients undergoing endocrine therapy between T stage subgroups. Adjuvant chemotherapy was given to 61 (16.3%) patients. Forty-two patients, 34.4% of the patients with ER and PR negative disease, received adju- vant chemotherapy. An anthracycline-based regimen was given to thirty-three patients (54.1% of these 61 patients), and 25 patients were treated with combination