Benign and malignant mast cell proliferations. Diagnosis and separation using a pH-dependent toluidine blue stain in tissue section.

Using a pH-adjusted toluidine blue stain (pH range, 2.5-6.5), we sequentially examined the staining patterns of mast cells in tissue sections taken from patients with localized or reactive mast cell lesions and benign or malignant mastocytosis syndromes. Reactive or benign lesions stained well over the entire range of pHs and were separated from malignant mast cell proliferations which stained poorly and with greatest intensity in the less acidic range (pH greater than 3.5). Patients with disseminated mast cell lesions but without tumor masses or leukemia had a staining pattern between that of benign and malignant lesions. Basophils stained intensely at pH 2.5, and metachromasia rapidly diminished at higher pH. The use of the pH dependent toluidine blue stain may be an adjunct in recognizing patients with mast cell lesions, predicting their prognosis, and distinguishing basophils from mast cells.