Claudin-Low Breast Cancer; Clinical & Pathological Characteristics

Abstract

Claudin-low breast cancer is a molecular type of breast cancer originally identified by gene expression profiling and reportedly associated with poor survival. Claudin-low tumors have been recognised to preferentially display a triple-negative phenotype, however only a minority of triple-negative breast cancers are claudin-low. We sought to identify an immunohistochemical profile for claudin-low tumors that could facilitate their identification in formalin fixed paraffin embedded tumor material. First, an in silico collection of ~1600 human breast cancer expression profiles was assembled and all claudin-low tumors identified. Second, genes differentially expressed between claudin-low tumors and all other molecular subtypes of breast cancer were identified. Third, a number of these top differentially expressed genes were tested using immunohistochemistry for expression in a diverse panel of breast cancer cell lines to determine their specificity for claudin-low tumors. Finally, the immunohistochemical panel found to be most characteristic of claudin-low tumors was examined in a cohort of 942 formalin fixed paraffin embedded human breast cancers with >10 years clinical follow-up to evaluate the clinico-pathologic and survival characteristics of this tumor subtype. Using this approach we determined that claudin-low breast cancer is typically negative for ER, PR, HER2, claudin 3, claudin 4, claudin 7 and E-cadherin. Claudin-low tumors identified with this immunohistochemical panel, were associated with young age of onset, higher tumor grade, larger tumor size, extensive lymphocytic infiltrate and a circumscribed tumor margin. Patients with claudin-low tumors had a worse overall survival when compared to patients with luminal A type breast cancer. Interestingly, claudin-low tumors were associated with a low local recurrence rate following breast conserving therapy. In conclusion, a limited panel of antibodies can facilitate the identification of claudin-low tumors. Furthermore, claudin-low tumors identified in this manner display similar clinical, pathologic and survival characteristics to claudin-low tumors identified from fresh frozen tumor material using gene expression profiling.

Fig 1. Hierarchical Clustering of 1,593 breast tumor samples using the 60 genes identified as differentially expressed between CL tumors and tumors of all other molecular subtypes

Fig 2

Representative H&E stained image of luminal A [A], luminal B [B], HER2 [C], basal [D] and Claudin-low [E] tumors. ER staining in luminal A [F], luminal B [G], HER2 [H], basal [I] and Claudin-low [J] tumors. PR staining in luminal A [K], luminal B [L], HER2 [M], basal [N] and Claudin-low [O] tumors. HER2 staining in luminal A [P], luminal B [Q], HER2 [R], basal [S] and Claudin-low [T] tumors. Ki67 staining in luminal A [U], luminal B [V], HER2 [W], basal [X] and Claudin-low [Y] tumors. EGFR staining in luminal A [Z], luminal B [AA], HER2 [BB], basal [CC] and Claudin-low [DD] tumors. CK5 staining in luminal A [EE], luminal B [FF], HER2 [GG], basal [HH] and Claudin-low [II] tumors. Claudin-3 staining in luminal A [JJ], luminal B [KK], HER2 [LL], basal [MM] and Claudin-low [NN] tumors. Claudin-4 staining in luminal A [OO], luminal B [PP], HER2 [QQ], basal [RR] and Claudin-low [SS] tumors. Claudin-7 staining in luminal A [TT], luminal B [UU], HER2 [VV], basal [WW] and Claudin-low [XX] tumors. E-cadherin staining in luminal A [YY], luminal B [ZZ], HER2 [AAA], basal [BBB] and Claudin-low [CCC] tumors.

Fig 3. Disease-Free Survival (DFS) of Patients enrolled in the AHWBI trial by Tumor Subtype

Fig 4. Overall Survival (OS) of Patients enrolled in the AHWBI trial by Tumor Subtype

Fig 5. Local Recurrence (LR) of Patients enrolled in the AHWBI trial by Tumor Subtype