ALK and adenosquamous carcinoma: Although the true reason for the discrepancy outlined above remains unclear, there are two main possible explanations: (a) biological, ALK variant-related [12] or due to heterogeneity of staining, as this situation has been reported specially in SCC and adenosquamous carcinoma [13], [37]; and, (b) methodological, due to suboptimal pre-analytical or analytical phases as less sensitive detection systems may result in heterogeneous staining patterns [18].