ERBB2 and pachyonychia congenita: A large study analyzing over 2500 PC tissue samples in a microarray using IHC and FISH showed weak HER2 staining (<2+) in approximately 20% of samples and ERBB2 gene amplification in one sample; however, significant associations were found between positive staining and known prognostic parameters (high Gleason grade, advanced TNM stage, rapid tumor cell proliferation, and tumor recurrence) [9].