Introduction The number of cancer cases among the elderly continue to increase as the worldwide population ages. This patient subset is underrepresented in clinical trials, partly because of unresolved uncertainties about age-associated tolerabilities and antitumor activities. We reviewed phase 1 trial data to study tolerance and efficacy of novel agents used for treatment of elderly patients with cancer. Methods Data from 773 consecutive evaluable patients in 85 phase 1 clinical trials (2008-2016) at START Madrid-CIOCC were analyzed according to age, with respect to objective response, survival, and toxicity. Results The mean age was 58.7 (range: 18-87) years; 260 (33.6%) patients were >65 y (elderly group). One hundred thirty-seven (17.8%) patients received immunotherapy drugs, 308 (39.8%) received targeted agents, and 328 (42.4%) received chemotherapy. No statistically significant differences in overall survival, objective response, or severe toxicity rates were found according to treatment type. Similar toxicities and clinical activities were found between the two age subgroups; 18.8% of the elderly and 20.7% of the younger patients experienced severe hematological toxicity (p=0.5), and 30.2% and 32.7%, respectively, experienced severe non-hematological toxicity (p=0.4). Regarding antitumor activity, 12.4% of the elderly and 15% of the younger patients achieved objective responses (p=0.41). There were no significant between-group differences in overall survival (9.7 versus 11.5 months, respectively, p=0.1) or progression-free survival (2.3 versus 2.2 months, respectively, p=0.7). Conclusions This retrospective study found that elderly and younger populations had comparable antitumor activities and toxicity profiles. These results support including elderly patients with cancer in early-phase trials.