Prostate cancer; Pain in both legs in his thighs and calves; This spontaneous case was reported by a patient and describes the occurrence of PROSTATE CANCER (Prostate cancer) in a 78-year-old male patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 939903, 021C21A and 026B21A) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.     No Medical History information was reported.   On 09-Apr-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) 1 dosage form. On 07-May-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. On 01-Dec-2021, received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (Intramuscular) dosage was changed to 1 dosage form. On an unknown date, the patient experienced PROSTATE CANCER (Prostate cancer) (seriousness criterion medically significant) and PAIN IN EXTREMITY (Pain in both legs in his thighs and calves). The patient was treated with GABAPENTIN at an unspecified dose and frequency; TRAMADOL at an unspecified dose and frequency; PARACETAMOL (TYLENOL) at an unspecified dose and frequency; DILTIAZEM at an unspecified dose and frequency; VITAMIN C [ASCORBIC ACID] at an unspecified dose and frequency and COLECALCIFEROL (VITAMIN D [COLECALCIFEROL]) at an unspecified dose and frequency. At the time of the report, PROSTATE CANCER (Prostate cancer) and PAIN IN EXTREMITY (Pain in both legs in his thighs and calves) had not resolved.            The concomitant medication was not reported by reporter.  It was reported that after the 3rd dose of the vaccine patient diagnosed with prostate cancer and took radiation therapy. Patient had spoken with his cardiologist, urologist, and primary care physician about his symptoms which had continued up until today. Patient had also been offered surgery for his pain; however, he had declined. Patient's HCPs had not presented the idea that the symptoms could be the result of the vaccine.  Company comment: This spontaneous case concerns a 78-year-old male patient, with no reported medical history, who experienced the unexpected serious (medically significant) event of Prostate cancer on an un unknown date after receiving the 3rd dose of mRNA-1273 vaccine. Onset latency could not be determined as onset date of event was not provided. It was reported that after the 3rd vaccination, patient had pain on both legs (thigh and calves) and was diagnosed with prostate cancer and was taking radiation treatment. Patient consulted medical specialists. Patient took Gabapentin, Tramadol, Paracetamol, Diltiazem, and vitamins C and D. The outcome of event was reported as not resolved. Patient had received 1st and 2nd doses of mRNA-1273 vaccine 28 days apart. The 2nd dose was administered 6 months and 24 days prior to the 3rd dose of mRNA-1273 vaccine. The benefit-risk relationship of mRNA-1273 is not affected by this report. Event's seriousness was assessed based on medical judgement.; Sender's Comments: This spontaneous case concerns a 78-year-old male patient, with no reported medical history, who experienced the unexpected serious (medically significant) event of Prostate cancer on an un unknown date after receiving the 3rd dose of mRNA-1273 vaccine. Onset latency could not be determined as onset date of event was not provided. It was reported that after the 3rd vaccination, patient had pain on both legs (thigh and calves) and was diagnosed with prostate cancer and was taking radiation treatment. Patient consulted medical specialists. Patient took Gabapentin, Tramadol, Paracetamol, Diltiazem, and vitamins C and D. The outcome of event was reported as not resolved. Patient had received 1st and 2nd doses of mRNA-1273 vaccine 28 days apart. The 2nd dose was administered 6 months and 24 days prior to the 3rd dose of mRNA-1273 vaccine. The benefit-risk relationship of mRNA-1273 is not affected by this report. Event's seriousness was assessed based on medical judgement.