Box 45 continued

Suppose on one arm the response rates are similar, but only 80% of eligible patients (i.e. 40% rather than 50% of the total) proceed to the second randomization: Of300 patients,

♦ 150 will have progressive disease at twelve weeks, and 10% 18-month survival,

♦ sixty will be randomized to stop chemotherapy and will have 10% 18-month survival,

♦ sixty will be randomized to continue chemotherapy and will have 20% 18-month survival,

♦ thirty will choose not to enter the second randomization

(a) if they all choose to continue, 18-month survival would be 20% and the overall survival would be 13%,

(b) if they all choose to stop, 18-month survival would be 10% and the overall survival would be 12%.

Thus taking the extremes, the overall survival rates would vary by only ±0.5%

under review by the same data monitoring and ethics committee which was empowered to recommend modifications to the trial design if necessary.

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