Characteristics Age at entry, mean ± SD (n = 392) Tumor size, number (%) (n = 352) ≤ 15 m > 15 mm Multifocal Tumor grade*, number (%) (n = 388) I II III Detection mode, number (%) (n = 391) Screening Clinically Type of surgery, number (%) (n = 392) Breast Conserving Surgery Mastectomy Postoperative radiotherapy, number (%)(n = 392) Yes No Zhou et al. BMC Cancer 2010, 10:653 http://www.biomedcentral.com/1471-2407/10/653 Page 4 of 8 Table 1 Characteristics of DCIS molecular subgroups, by immunohistochemistry in 392 women with a primary DCIS Basal-like (n = 32, 8.2%) 56.7 ± 12.6 Non basal-like (n = 360, 91.8%) 57.8 ± 11.5 16 (59.3) 8 (29.6) 3 (11.1) 1 (3.1) 11 (34.4) 20 (62.5) 22 (68.8) 10 (31.3) 26 (81.3) 6 (18.8) 10 (31.3) 22 (68.8) 175 (53.9) 104 (32.0) 46 (14.2) 29 (8.2) 171 (48.0) 156 (43.8) 276 (76.9) 83 (23.1) 272 (75.6) 88 (24.4) 130 (36.1) 230 (63.9) P 0.6 0.84 0.11 0.3 0.61 0.72 * Tumor grade: DCIS were classified according to the European Organization for Research and Treatment of Cancer (EORTC) system. Kaplan-Meier analyses also showed a non-statistically higher risk for invasive- or general recurrence for the basal-like DCIS (p = 0.15) as seen in Figure 1b and the p-value for women undergoing BCS was 0.16. 2.3 Triple-negative group vs. non triple-negative group We also assessed the prognostic implications of triple-negative (ER-, PR- and HER2-negative) vs. non triple-negative DCIS. Of all 458 women, 409 could be classified. Thirty two were classified as triple-negative and 377 as not. Triple-negative tumors had a HR of 1.1 (95% CI, 0.4-2.7) and 1.1 (0.4-2.9) for local recurrence compared with the non triple-negative in the univariate and multivariate analyses, respectively. The adjusted HR for an invasive- or general recurrence in the triple-nega- tive group compared with women in non triple-negative was 1.4 (0.5-4.0) and 1.6 (0.6-4.8). Kaplan-Meier analyses showed no statistically signifi- cantly higher risk for local recurrence or invasive- or general recurrence for the triple-negative DCIS, neither in the subset of women undergoing BCS (p = 0.86 and 0.25 respectively) nor including all women (p = 0.67 and 0.44 respectively). (Table 2 and Figure 2a-b). Of the 392 women with complete IHC data, 32 were classified as basal-like and 32 as triple-negative. How- ever, only 24 women were classified as both basal-like and triple-negative. These subgroups were too small to do any statistical analyses on but during the follow-up, the 8 women who were basal-like and non triple- negative had four invasive- or general recurrences and the 8 women who were triple-negative and non basal- like only had one invasive recurrence. Discussion We have conducted a population-based study of primary DCIS to assess the association between an IHC surro- gate basal-like DCIS genotype and prognosis. Our results showed that basal-like DCIS had a higher risk of local recurrence and a higher risk of developing invasive cancer compared to other DCIS. The risk was almost doubled but this was not statistically significant. In our study, we defined basal-like DCIS as those that were ER-negative, HER2-negative, but positive for either CK 5/6 or EGFR. Nielsen et al [19], who proposed these criterions in 2004 for invasive breast cancer, found that defining basal-like breast cancer in this way resulted in 76% sensitivity and 100% specificity, when the gene expression signature was used as gold standard. Abd El-Rehim et al., [28] studied over 1000 cases of invasive breast cancer with 26 IHC markers and identified 6 clusters of tumors. Five of these clusters roughly corre- sponded to the 5 subtypes identified earlier; the remain- ing group consisted of only 4 cases. Livasy et al., [18] then verified and confirmed the criteria in DCIS tumors. Today, IHC is increasingly used as a surrogate for mole- cular gene profiling since it allows classification of tumors at an affordable costs and in the absence of fresh tissue speciments [29]. Moreover, these four sub- groups have distinguishing features closely associated with subtypes defined by gene expression profiling, including distinct clinical outcomes [30]. A possible cause of subtype misclassification is the HER2 status based on IHC scoring. We assessed the sta- tus of HER2 by SISH and used IHC only in those cases