Periodic acid-Schiff reaction changes during the course of relapsing lymphoblastic leukaemia.

Bone marrow smears taken at diagnosis and subsequent haematological relapse from 41 patients with lymphoblastic leukaemia (ALL) were compared to assess the proportion of blast cells showing a positive periodic acid-Schiff (PAS) reaction at different stages of the same disease. 20 patients never displayed more than 10% PAS positive blasts at any stage, and of these 8 never had any PAS positivity at all. 7 patients maintained a proportion of PAS positive cells over 10% of the total but with no loss or gain in the numbers of such cells. 14 patients showed a significant change in the PAS reaction during the course of their disease, 7 showing a marked reduction in PAS positive cells, and 7 showing an equally marked increase. From these results it seems that the PAS reaction does not identify a sub-type of ALL or mark the degree of differentiation of a given case. It could be indicative of a specific stage of the lymphoblast mitotic cycle.