A proposal of indices to describe the carcinoembryonic antigen time course in in order to assess the effects of treating recurrent colo-rectal carcinoma.

In order to assess the effects of treating recurrent or non-resectable colo-rectal cancer, the following 5 indices for the serum CEA time course were devised: 1. If the serum CEA doubling time is altered by any treatment from D1 to D2 we term D2/D1 as the "CEA doubling time ratio" of the treatment; 2. the per cent decrease in the serum CEA level from CEA1 to CEA2 is calculated by (logCEA1 - logCEA2) X 100/logCEA1; 3. the period when the CEA level has returned to normal after a treatment is termed the "normalization period"; 4. "backward time retrieval" is the period between the lowest point of the posttreatment CEA and the crossing-point of this level by the pretreatment rising slope and; 5. "forward time earning" can also be defined. By using these indices, surgical treatments resulted in a higher per cent decrease in CEA, a longer normalization period but a shorter doubling time when the tumor recurred.