FOLH1 and neoplasm: This latter moiety has driven the search for agents that will deliver the cytotoxic component to unique markers of tumours such as prostate specific membrane antigen or over-expressed folate receptor (FR).1 Indeed, the FR has proven highly successful in targeting studies, benefiting from an overexpression in certain tumor lines and the high binding affinity of FR (KD ~ 0.42 × 109 M) for folate.2