Tumour regression after endostatin therapy

It was with great interest that we read the report1 on the lack of acquired drug resistance to repeated doses of endostatin in experimental cancers in mice. Of particular interest is the unprecedented finding that each tumour type became indefinitely dormant after a varying number of treatment cycles. We believe one explanation for this phenomenon might be found in the clinical observation that, after complete regression of large bulky tumours, rebiopsy of the primary tumour site will frequently show large amounts of fibrosis or scarring.