Macroscopic, microscopic and immune histological appearance of an oral lichen planus and a subsequently arising squamous cell carcinoma. Macroscopic (A) and microscopic (B) picture of the squamous cells carcinoma. p53 expression (C to E, single positive cells are indicated by arrows), Erk 1/2 phosphorylation (F to H, increased expression is indicated by closed triangles) and Bax expression (I to K, reduced expression is indicated by open triangles) in mucosa before (C, F, I) and after (D, G, J) tacrolimus treatment, as well as in the arising squamous cell carcinoma (E, H, K); magnification: A 5×, C to K 20×. All lesions were obtained by surgical excision, fixed in formalin and embedded in paraffin. Five μm sections of tumor lesions were fixed in acetone and air dried for 30 min. Slides were incubated for 30 min with the indicated specific primary antibodies (anti-p53 [clone D07] and anti-Bax [polyclonal], DAKO, Hamburg, Germany; anti-pErk 1/2 [clone E10], Cell Signalling, BioLabs New England, Frankfurt, Germany) at predetermined dilutions ranging from 1:200 to 1:800.