PERIODIC ACID-SCHIFF REACTION IN CHILDHOOD LYMPHOBLASTIC-LEUKEMIA

Aims-To assess the prevalence and degree of periodic acid Schiff (PAS) positivity in blast cells from children with lymphoblastic leukaemia (ALL); its association with other disease characteristics; and its cli nical importance in predicting the outcome of treatment. Methods-Marro w slides from entrants to a large United Kingdom multicentre ALL trial (UKALL X) were batch processed and assessed blind for PAS positivity by one morphologist. Patients were classified into groups A, B, and C, corresponding to less than 1% PAS positive cells, 1-10%, and over 10% , respectively. Their PAS pattern was then compared with other clinica l and pathological features of ALL and with treatment outcome. Results -Slides from 921 children were examined of which 371 (40%) were catego rised as group A, 324 (35%) as group B, and 226 (25%) as group C. Ther e was a clear association between the presence of blast cell vacuoles on Romanowsky staining and PAS positivity. Group A (PAS negative) pati ents included a disproportionate excess of those with L2 morphology, t hose under 2 or over 6 years of age, those with an initial white cell count over 50 x 10(9)/1, those with a T or null cell immunophenotype, and those with chromosomal abnormalities other than ''high hyperdiploi dy)). Four years from diagnosis, group C patients had an 8% disease fr ee survival advantage over those in group A (2p = 0.01). This was irre spective of initial white cell count, but not of immunophenotype or th e presence of vacuoles. Conclusions-Strong PAS positivity is a feature of ''common'' ALL and is particularly associated with blast cell vacu oles. It does occasionally occur in other disease subtypes with or wit hout vacuoles. It predicts a better response to current treatment, but not independently of other cell characteristics.