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Cross-Trial Comparisons in the Oncology Arena: When Is This Justified?

A classic example of this highly relevant clinical phenomenon is provided by the initial, and subsequent, phase 3 randomized trials employing the then novel regimen of cisplatin plus paclitaxel in the treatment of advanced stage epithelial ovarian cancer [3, 4] . In the first trial, conducted by the Gynecologic Oncology Group (USA), the median progression-free and overall survivals of this relatively large population treated with cisplatin plus paclitaxel were 18 and 38 months, respectively [3] . However, when the exact treatment regimen ( drugs, doses, schedules) was employed by the same group of oncologists in their next trial, the identical patient population (tumor stage, grade, age, etc.) was found to experience a rather striking reduction in clinical outcome (median progression-free and overall survivals, 14 and 27 months, respectively) [4] . While it is not possible to know precisely why the treated ‘populations’ (as opposed to any individual ovarian cancer patient managed with cisplatin plus paclitaxel) experienced such different outcomes, one can speculate that increasing physician comfort with the potential toxicities of this drug combination (based on the results of the initial landmark study [3] ) led to subsequent study entry of individuals with greater co-morbidity (including histories of pre-existing cardiac dysfunction) and a more It is appropriately appreciated that there are inherent dangers associated with any attempt to directly compare the outcomes observed in independently conducted clinical trials. This is particularly problematic in the oncology arena where it is recognized there is frequently tremendous heterogeneity within patient populations as regards well-defined and currently poorly understood disease characteristics [1] . Further, populations differ in pre-existing co-morbidity, and outcomes may be substantially influenced by provider/institutional skills (particularly in the realm of surgery or technically demanding procedure-oriented medical care) [2] . In the absence of randomization within a single trial, where specific efforts are unable to be employed to ‘control’ for such variations (e.g. tumor grade, age, performance status, etc.) it is far more than a theoretical possibility that any observed differences in outcomes associated with employing different research strategies in ‘identical’ patient populations (tumor type and stage) will actually be due to relevant (but possibly not appreciated) differences in the specific patient populations who were entered into the individual studies, rather than to the superiority (or conversely, inferiority) of one management approach compared to an alternative. Received: January 21, 2011 Accepted: January 21, 2011 Published online: June 14, 2011 Oncology