Rare disease

With uncommon diseases, randomized trials are difficult, and inevitably smaller than might be considered ideal. In introducing an experimental treatment in this kind of setting, knowing that there may only be one chance to conduct a randomized trial, unequal randomization can be valuable. For example, in the late 1980s discussions took place about a randomized trial of chemotherapy for primary cerebral lymphoma. Standard treatment for these patients was surgery and radiotherapy and there was considerable experience with this approach. The question of interest was whether adding chemotherapy could improve survival, but there was little experience with the particular chemotherapy regimen of interest in this setting. Here, the total number of patients was limited by the rarity of the disease. However, a 2 : 1 allocation to chemotherapy was employed. This only slightly reduced the overall power of the comparison compared with a 1: 1 randomization in the same number of patients, but enabled more experience to be gained with the experimental treatment, more data on toxicity, and to obtain a more precise estimate of the survival rates associated with this treatment [14].

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