PTEN and B-cell non-Hodgkin lymphoma: The complicated pattern of association between PIK3CA and PTEN mutations identified here also suggests caution in evaluating clinical studies based on an assessment of PTEN protein; for instance, other work has identified mutual exclusion between PIK3CA and PTEN mutations in B cell lymphoma, in part based on immunohistochemical evaluation of PTEN protein expression - an approach biased to detect cases of PTEN deletion (discussed in refs. 71,72).