Myocarditis; Reoccurrence of cancer. This developed around heart.; Dose 1 and Dose 2 with Pfizer/Biontech and Dose 3 Moderna; Dose 1 and Dose 2 with Pfizer/Biontech and Dose 3 Moderna; This spontaneous case was reported by a patient and describes the occurrence of RECURRENT CANCER (Reoccurrence of cancer. This developed around heart.) and MYOCARDITIS (Myocarditis) in a 68-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.     The patient's past medical history included Heart failure in November 2018, Left ventricular enlargement in November 2018 and Cancer. Previously administered products included for Drug use for unknown indication: Rituxan on 17-Apr-2018, Rituxan on 17-Apr-2018, Rituxan on 17-Apr-2018, Rituxan on 24-Apr-2018, Rituxan on 24-Apr-2018, Rituxan on 24-Apr-2018, Rituxan on 02-May-2018, Rituxan on 02-May-2018, Rituxan on 02-May-2018, Rituxan on 08-May-2018, Rituxan on 08-May-2018, Rituxan on 08-May-2018, Pfizer/Biontech (Dose: 1, Lot number: EN6203) on 03-Mar-2021, Pfizer/Biontech (Dose: 2 and Lot number: ER8734) on 30-Mar-2021. Past adverse reactions to the above products included Cognitive function abnormal with Rituxan, Rituxan, Rituxan and Rituxan; Fatigue with Rituxan, Rituxan, Rituxan and Rituxan; No adverse event with Pfizer/Biontech and Pfizer/Biontech; and Shortness of breath with Rituxan, Rituxan, Rituxan and Rituxan.    On 23-Sep-2021, the patient received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 23-Sep-2021, the patient experienced INTERCHANGE OF VACCINE PRODUCTS (Dose 1 and Dose 2 with Pfizer/Biontech and Dose 3 Moderna) and COVID-19 IMMUNISATION (Dose 1 and Dose 2 with Pfizer/Biontech and Dose 3 Moderna). In March 2022, the patient experienced RECURRENT CANCER (Reoccurrence of cancer. This developed around heart.) (seriousness criterion medically significant). On an unknown date, the patient experienced MYOCARDITIS (Myocarditis) (seriousness criterion medically significant). The patient was treated with RITUXIMAB (TRUXIMA [RITUXIMAB]) on 10-May-2022 for Recurrent cancer, at an unspecified dose and frequency; RITUXIMAB (TRUXIMA [RITUXIMAB]) on 07-Jun-2022 for Recurrent cancer, at an unspecified dose and frequency and RITUXIMAB (TRUXIMA [RITUXIMAB]) on 07-Jul-2022 for Recurrent cancer, at an unspecified dose and frequency. At the time of the report, RECURRENT CANCER (Reoccurrence of cancer. This developed around heart.), MYOCARDITIS (Myocarditis), INTERCHANGE OF VACCINE PRODUCTS (Dose 1 and Dose 2 with Pfizer/Biontech and Dose 3 Moderna) and COVID-19 IMMUNISATION (Dose 1 and Dose 2 with Pfizer/Biontech and Dose 3 Moderna) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In November 2018, Ejection fraction: Ejection percent of 35 to 40 percent. On an unknown date, Ejection fraction: dropped 5-10 percent, down to 15 percent.         No concomitant medications were reported. On 27-Jan-2022, the patient contacted his cancer doctor to get permission to take Methotrexate for 5-6 months to treat myocarditis of his heart. This medical issue occurred, and treatment took place just prior to findings of cancer active around his heart and aorta. This was his 2nd round of immunotherapy. Reported that after each treatment with Truxima the ejection fraction of patient dropped from 05-10 percent down to 15 percent EF. Patient was not able to continue the treatment at the time of report. Patient reported that growth appear around his heart and aorta.  Company Comment: This is a spontaneous case concerning a 68 year-old, male patient with a history of cancer, who experienced the serious (due to medically significant) expected, AESI of myocarditis and the serious (due to medically significant) unexpected, event of recurrent cancer (location reported as around the heart), which occurred after the mRNA-1273 vaccine, received as the third dose of COVID-19 vaccination schedule. The event recurrent cancer occurred approximately 6 months after vaccination. Patient received treatment with rituximab. The outcome of both events was not reported. The mentioned medical history remains as a risk factor for the event recurrent cancer, since reocurrence is part of its natural history. Additionally, Interchange of vaccine products and Revaccination with different COVID-19 vaccine (vaccination with two doses of COVID-19 vaccine Tozinameran) was noted in the case. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.