This spontaneous case was reported by a patient and describes the occurrence of NEOPLASM MALIGNANT (Cancer) in a 79-year-old female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination. The occurrence of additional non-serious events is detailed below. The patient's past medical history included Surgery in June 2021. Concurrent medical conditions included Immunocompromised. In January 2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. In January 2021, the patient experienced NEOPLASM MALIGNANT (Cancer) (seriousness criterion medically significant) and UNDERDOSE (Her first dose was in January 2021, but it was only half a dose). At the time of the report, NEOPLASM MALIGNANT (Cancer) and UNDERDOSE (Her first dose was in January 2021, but it was only half a dose) outcome was unknown. The action taken with mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown) was unknown. No concomitant medications were reported. The patient's first dose was in January 2021, but it was only half a dose because they said the full dose would give bad side effects to immunocompromised individuals. The patient had cancer and surgery in Jun 2021. Patient had her boosters of 50 mcg in September 2021 and March 2022. Then she states that she didn't she had cancer in January 2021. Her memory fails her now, if her first two doses were at half dose. No treatment medications were reported. Company comment: This spontaneous case concerns a 79-year-old female patient with relevant medical history of immunocompromised status reported, who experienced the unexpected serious (medically significant) event of Neoplasm malignant that occurred on an unknown date after first dose of mRNA-1273 vaccination. Latency cannot be assessed since vaccination date nor event onset date was disclosed. Patient had cancer and surgery in June 2021. Additionally, Under dose was reported. Her first dose was in January 2021, but it was only half a dose because they said the full dose would give bad side effects to immunocompromised individuals. She has had 2 primary doses and 2 boosters at 50%. No further information on risk factors, detailed clinical course, investigations, treatment of the events was available in the report. Outcome of the events was not known at the time of report. Relevant medical history could be confounding for the event. The benefit-risk relationship of mRNA-1273 Vaccine is not affected by this report. Event seriousness assessed as per medical judgement. Sender's Comments: This spontaneous case concerns a 79-year-old female patient with relevant medical history of immunocompromised status reported, who experienced the unexpected serious (medically significant) event of Neoplasm malignant that occurred on an unknown date after first dose of mRNA-1273 vaccination. Latency cannot be assessed since vaccination date nor event onset date was disclosed. Patient had cancer and surgery in June 2021. Additionally, Under dose was reported. Her first dose was in January 2021, but it was only half a dose because they said the full dose would give bad side effects to immunocompromised individuals. She has had 2 primary doses and 2 boosters at 50%. No further information on risk factors, detailed clinical course, investigations, treatment of the events was available in the report. Outcome of the events was not known at the time of report. Relevant medical history could be confounding for the event. The benefit-risk relationship of mRNA-1273 Vaccine is not affected by this report. Event seriousness assessed as per medical judgement.