Cytologic abnormalities of mast cells in MCL. Mast cells from MCL range from mature mast cells (A-D) to more immature cells with (E-I) promastocytes and (J-K) even metachromatic or (K) ungranulated blasts. (A-B) Circulating round mast cells; (C) spindle-shaped mast cell; (D) packed and polar granule aggregates; (E-G) degranulated/hypogranulated promastocytes; (H-I) coalescent granules; (I) lacunar cytoplasmic areas; (J-K) undifferentiated immature cells with metachromatic granules and prominent nucleoli.