Fig. 4

CD1a immunohistochemistry FFPE tissue section from LCH patients stained with CD1a. (a) Two samples that were V600E mutation (+) after both primary PCR amplification and TspRI followed by additional PCR amplification. Four of five samples in this category demonstrated up to 70 % tumor content. These cases were easy to detect by primary PCR. (b) Examples of staining of samples that were BRAF mutation (-) after primary PCR, but mutation (+) after TspRI treatment. Seven of eight such samples contained <50 % tumor content. These samples were not dissected to isolate tumor tissue; nevertheless, a BRAF V600E mutation was detected after treatment with TspRI. (c) Two samples that were BRAF V600E mutation (-) after both primary PCR and after TspRI digestion followed by additional amplification. Tumor content was determined in 11 of 13 samples in this category and ranged from 4.9 to 100 %, hence mutation detection was independent of tumor content