Power outages affected services at the Hannibal Regional Health Care System.
The system lost power to five buildings including its cancer, children's and vision centers, vice president of facilities Doug Ruble said.
Oncology patients were re-routed to the Hannibal Clinic for treatment.
The main hospital didn't lose power during Monday's storm.
Patients were notified by telephone if they needed to adjust their appointments and treatment.
Ruble said if power returns this evening, the cancer treatment center would reopen as early as Thursday afternoon.