Abstract P3-06-39: Anaplastic lymphoma kinase (ALK) protein overexpression is not a feature of inflammatory breast cancer
Authors: Colpaert Cecile , Marsan Melike , Vermeulen Peter , Dirix Luc , Van Laere Steven ,   Inflammatory Breast Cancer International Consortium
Published: May 2015

Recent studies suggest that anaplastic lymphoma kinase (ALK) could serve as a therapeutic target for inflammatory breast cancer (IBC) and that strategies targeting ALK should be considered for evaluation in clinical trials. Reverse phase protein arays revealed activation of the ALK receptor tyrosine kinase and biochemically-linked downstream signalling molecules in pre-clinical models of IBC. ALK genetic abnormalities have been reported in 80% (20/25) of IBC patients with a high prevalence of ALK alterations in basal-like IBC (Robertson F. et al., 2013). However, ALK protein expression has not been studied in human IBC samples.

Immunohistochemical detection of the ALK protein is increasingly being used as a screening tool to test samples for ALK rearrangements. The biological premise is that the genetic abnormality of the ALK gene leads to overexpression of the ALK protein and therefore overactivity of the ALK tyrosine kinase; since this kinase is the target of crizotinib, it makes sense to assess the drug target directly.

Formalin fixed paraffin embedded tissue samples from pre-treatment surgical biopsies of 79 consecutive IBC patients were immunohistochemically (IHC) tested for ALK protein over-expression using a validated IHC test (NCL-ALK, clone 5A4) with a sensitivity of 93% and a specificity of 100% when the Vysis ALK-FISH break apart test is used as a gold standard. Stained tissue sections were evaluated using the IHC histoscore proposed by Thunnissen E. et al., 2012, assessing both the proportion of tumor cells showing cytoplasmic staining and the staining intensity. Cytoplasmic staining of appendiceal ganglion cells was used as an on-slide external positive control; weak to moderate cytoplasmic staining of macrophages was used as an internal positive control.

In 75 of the 79 tissue samples none of the tumor cells showed any ALK immunoreactivity. One tumor showed moderate cytoplasmic staining in a few cells (&lt;1%, score 2+); ALK (2p23) FISH showed no rearrangement. This tumor was hormone receptor negative and HER2 negative. Three tumors showed minimal cytoplasmic staining in a few cells (&lt;1%, score 1+).

These results demonstrate that ALK protein overexpression is not a feature of IBC. Although genetic abnormalities of ALK without protein overexpression are not excluded, our results show that ALK IHC cannot be used to identify IBC patients eligible for enrollment in clinical trials evaluating ALK targeted therapeutics.

Citation Format: Cecile Colpaert, Melike Marsan, Peter Vermeulen, Luc Dirix, Steven Van Laere, Inflammatory Breast Cancer International Consortium. Anaplastic lymphoma kinase (ALK) protein overexpression is not a feature of inflammatory breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-06-39.