Extensive disease small cell lung cancer dose-response relationships: implications for resistance mechanisms.
BACKGROUND
Some studies (but not others) suggested that high doses are beneficial in small cell lung cancer (SCLC). We hypothesized that dose-response curve (DRC) shape reflects resistance mechanisms.


METHODS
We reviewed published SCLC clinical trials and converted response rates into estimated mean tumor cell kill, assuming killing is proportional to reduction in tumor volume. Mean % cell survival was plotted versus planned dose intensity. Nonlinear and linear meta-regression analyses (weighted according to the number of patients in each study) were used to assess DRC characteristics.


RESULTS
Although associations between dose and cell survival were not statistically significant, DRCs sloped downward for five of seven agents across all doses and for all seven when lowest doses were excluded. Maximum mean cell kill across all drugs and doses was approximately 90%, suggesting that there may be a maximum achievable tumor cell kill irrespective of number of agents or drug doses.


CONCLUSIONS
Downward DRC slopes suggest that maintaining relatively high doses may possibly maximize palliation, although the associations between dose and slope did not achieve statistical significance, and slopes for most drugs tended to be shallow. DRC flattening at higher doses would preclude cure and would suggest that "saturable passive resistance" (deficiency of factors required for cell killing) limits maximum achievable cell kill. An example of factors that could flatten the DRC at higher doses and lead to saturable passive resistance would be presence of quiescent, noncycling cells.
Stewart
David J
DJ
Department of Thoracic/Head and Neck Medical Oncology, University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA. dstewart@mdanderson.org
Johnson
Constance
C
Lopez
Adriana
A
Glisson
Bonnie
B
Rhee
Jay M
JM
Bekele
B Nebiyou
BN
D000970:Antineoplastic Agents / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000473:pathology; D015201:Meta-Analysis as Topic; D009367:Neoplasm Staging; D055752:Small Cell Lung Carcinoma / Q000188:drug therapy* / Q000473:pathology; D015996:Survival Rate; D016896:Treatment Outcome
D000970:Antineoplastic Agents