Cytology L1 L2 L3 Cell size Small Large Large Nuclear chromatin Fine or clumped Fine Fine Nuclear shape Regular, may have cleft or indentation Irregular, may have cleft or indentation Regular, oval to round Nucleoli Indistinct or not visible One or more per cell; large, prominent One or more per cell; large, prominent Amount of cytoplasm Scanty Moderately abundant Moderately abundant Basophilia of cytoplasm Slight Slight Prominent Cytoplasmic vacuolation Variable Variable Prominent

Table 1: FAB classification of ALL The most helpful features for differentiating subtypes is in bold type.