Prediction of the radioresponse of individual tumors has been described as the Holy Grail of radiotherapy (1). An extensive literature on Holy Grail research suggests that those who sought it had no idea what they were looking for and, not surprisingly, that they never found it. The radiobiologists and radiation oncologists who met in Montreal on October 6–8, 1999, to address the topic of “The Prediction of Tumor Response to Therapy” were a more focused group with better prospects for eventual success.

A number of studies have been published of predictive assays based on clonogenic or nonclonogenic determination of tumor cell survival after a test dose of radiation. The first speaker, Catharine M. L. West (Paterson Institute for Cancer Research, Manchester, UK), proposed in situ immunohistochemical detection of tumor protein expression as an attractive alternative to cell-based assays. Immunohistochemistry has the potential to...

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