Natural Killer Cells and the Guy's Hospital Trials-Reply

In Reply.—Dr Evans suggests that cancer patients with low levels of NK cytotoxicity have developed distant metastases (presumably undetected) at the time of their original surgery. Although his comments refer to malignant lesions of the breast, this very attractive hypothesis can be tested to some extent in patients with colorectal cancer by reexamining the data from our original study. According to his hypothesis, patients presenting with low NK cytotoxicity are at increased risk of distant recurrence, but not of local recurrence, compared with patients with normal levels. Indeed, the risk of distant recurrence was 21% among patients with low preoperative NK cytotoxicity (