A single scale for comparing dose-intensity of all chemotherapy regimens in breast cancer: summation dose-intensity

To construct a single scale for comparing the dose-intensity of all chemotherapy regimens in breast cancer.

First-line single-agent trials in metastatic disease were reviewed. The unit dose-intensity (UDI) that was required to produce a 30% complete response plus partial response (CR + PR) rate was determined for each drug. Randomized trials were then analyzed that prospectively tested dose-intensity. The dose-intensities of the drugs in each arm were expressed as fractions of their UDIs and added together. This yielded each arm's summation dose-intensity (SDI), which was then correlated with treatment outcomes.

In the single-agent trials, dose-response relationships were linear when the studies covered a range of dose-intensities. In the randomized trials that tested dose-intensity in metastatic disease, response rates and median survival correlated linearly with the SDIs of the treatment arms. An increment of one SDI unit increased CR + PR rate by approximately 30%, CR rate by 10%, and median survival by 3.75 months. Metastatic disease trials were negative if the difference between the arms was less than 0.54 SDI units. Adjuvant trials that tested a dose-intensity difference of less than 0.65 SDI units were also negative.

A single-agent dose-response database can be derived from historic literature that enables comparison of the dose-intensity of all combination regimens on one scale. The dose-intensity increase required to improve outcome can then be identified in earlier trials that tested that variable. SDI methodology should be tested prospectively in contemporary patients, and may be useful in guiding dosage increases beyond the conventional range.