Specialist oncology pharmacists are being trained in Japan to assist cancer treatment teams. These specialized pharmacists address patients’ physical and mental problems in pharmacist-managed cancer care clinics, actively participate in formulating treatment policies, and are beneficial in offering qualitative improvements to patient services and team medical care. However, the effect of outpatient treatment by oncology pharmacists on therapeutic outcomes and medical costs is still unknown. A retroactive comparative analysis of the treatment details and clinical course was conducted among three groups of patients: patients who underwent adjuvant chemotherapy managed by a gynecologic oncologist only (S arm), patients managed by a non-oncologist (general practice gynecologist) only (NS arm), and patients managed by both a non-oncologist and a specialist oncology pharmacist (NS+Ph arm). The medical cost per course was significantly lower for patients in the NS+Ph arm than for those in the other two arms. Surprisingly, the outpatient treatment rate in the NS+Ph arm was overwhelmingly high. The involvement of an oncology pharmacist did not make a significant difference in therapeutic outcomes such as recurrence rate and survival. The participation of oncology pharmacists in the management of cancer patients undergoing chemotherapy enables safe outpatient treatment and also reduces medical costs.