breast cancer; This spontaneous case was reported by a patient and describes the occurrence of BREAST CANCER FEMALE (breast cancer) in a female patient of an unknown age who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 030M20A and 042L20A) for COVID-19 vaccination.     No Medical History information was reported.   On 24-Jan-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 21-Feb-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 01-Nov-2021,  after starting mRNA-1273 (Moderna COVID-19 Vaccine), the patient experienced BREAST CANCER FEMALE (breast cancer) (seriousness criterion medically significant). The patient was treated with PEMBROLIZUMAB (KEYTRUDA) for Breast cancer female, at a dose of 3 infusions every 3 weeks; PACLITAXEL (TAXOL) for Breast cancer female, at an unspecified dose and frequency; CARBOPLATIN (CARBO [CARBOPLATIN]) for Breast cancer female, at an unspecified dose and frequency and Immunotherapy for Breast cancer female. At the time of the report, BREAST CANCER FEMALE (breast cancer) outcome was unknown.            No concomitant information were reported by the reporter. Dose number 3 of Moderna vaccine, Lot number: 939909, Dose: unknown, Date administered: 04-Dec-2021. It was reported that on 01-Nov-2021, patient was diagnosed with breast cancer, so she received the treatment for that. She got the two primary series and a booster. She skipped a second booster. Now, she was almost completed the immunotherapy, so she can go get the booster. She was due for an appointment for her annual visit on 03-Nov-2022. She will probably be offered the regular flu shot and a third COVID booster. The patient started off with Taxol and Carbo and Keytruda when she was diagnosed with breast cancer. She had 3 infusions left of Keytruda (She gets it every 3 weeks. Last one was due 06-Dec-2022).  Company comment: This spontaneous case concerns a female of unknown age with no reported medical history who experienced the unexpected, serious (medically significant) event of breast cancer which occurred 8 months 11 days after receiving a dose of mRNA1273 as second dose in the COVID-19 vaccine series. The patient is currently on treatment for breast cancer with Pembrolizumab (Keytruda), Paclitaxel (Taxol) and Carboplatin (Carbo). Further details regarding the clinical course and diagnostic procedures done were not provided. The patient's gender is a pre-disposing risk factor for breast cancer. Information on other COVID-19 vaccine were not mentioned. The benefit-risk relationship of mRNA-1273 is not affected by this report. Sender's Comments: This spontaneous case concerns a female of unknown age with no reported medical history who experienced the unexpected, serious (medically significant) event of breast cancer which occurred 8 months 11 days after receiving a dose of mRNA1273 as second dose in the COVID-19 vaccine series. The patient is currently on treatment for breast cancer with Pembrolizumab (Keytruda), Paclitaxel (Taxol) and Carboplatin (Carbo). Further details regarding the clinical course and diagnostic procedures done were not provided. The patient's gender is a pre-disposing risk factor for breast cancer. Information on other COVID-19 vaccine were not mentioned. The benefit-risk relationship of mRNA-1273 is not affected by this report.