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Volume 13 Supplement 2

IX Madrid Breast Cancer Conference

Getting deep in the luminal B breast cancer subtype and its ki67 cut-off value


Inside the luminal breast cancer (BC) group, the B subclass carries a worse prognosis and is less responsive to hormonal treatment. Identification of the luminal B group, by Sørlie and colleagues [1], has been less consistent than other subclasses; and gene signatures based in estrogen-related genes or proliferation are better to identify this BC subclass. Cheang and colleagues genetically evaluated 144 luminal ER-positive HER2-negative tumors by IHC; they found a ki67 cutoff value of 13.25% to differentiate B from A subclasses [2]. No differentiation for PR status was done. The luminal B subgroup is usually defined as ki67 >13 if ER-positive, as well as HER2-positive or PR-negative. The target of this abstract is to evaluate behavior of different luminal B subsets.


We reviewed early BC cases evaluated at Hospital 12 de Octubre between 1995 and 2007 and selected 710 initially operated luminal B BC. We divided this group into four subsets as shown in Table 1 and analyzed their clinical-pathologic features and outcomes. Additionally, we evaluated the prognostic behavior of lowering the ki67 cutoff in the ER+PR+HER2- group (820 patients).

Table 1


The median ki67 value for the ER+PR- group was 17%. A ki67 cutoff at 14% discerns two groups of different prognosis inside the luminal group (extracting HER2+ and PR-); and comparison of ki67 cutoff between 14 and 11% found overlapped CI (median: 6.31 (5.99 to 6.62) vs. 6.49 (6.21 to 6.78)). Table 1 summarizes different characteristics and prognosis based on molecular features (statistical comparisons exclude the ER-PR+ subgroup).


Subsets inside the luminal B subtype according to expression of HER2, ER, PgR and ki67 have different features and behaviors. In the ER+PR+HER2- subgroup, ki67 cutoff should be re-evaluated in order to avoid misclassification and subsequent under-treatment of poorer prognosis tumors as luminal A hormono-sensitive phenotype.


  1. Sørlie T, Tibshirani R, Parker J, Hastie T, Marron JS, Nobel A, et al: Repeated observation of breast tumor subtypes in independent gene expression data sets. Proc Natl Acad Sci USA. 2003, 100: 8418-8423. 10.1073/pnas.0932692100.

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  2. Cheang MCU, Chia SK, Voduc D, Gao D, Leung S, Snider J, et al: Ki67 index, HER2 status, and prognosis of patients with luminal B breast cancer. J Natl Cancer Inst. 2009, 101: 736-750. 10.1093/jnci/djp082.

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Ciruelos, E., Castaneda, C., Pascual, T. et al. Getting deep in the luminal B breast cancer subtype and its ki67 cut-off value. Breast Cancer Res 13 (Suppl 2), P6 (2011).

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