patient first had breast cancer 10 years ago/The breast cancer returned in August 2021 to her left breast; sore right arm for 2 days after her second dose; This spontaneous case was reported by a consumer and describes the occurrence of BREAST CANCER RECURRENT (patient first had breast cancer 10 years ago/The breast cancer returned in August 2021 to her left breast) in a 78-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 Lymphadenectomy (10 Lymph nodes removed from her left breast and left shoulder.), Lymphadenectomy (10 Lymph nodes removed from her left breast and left shoulder.) and Radiation therapy (Patient also had radiation treatment in January 2022, which resolved the second recurrence of her breast cancer.) in January 2022. Concurrent medical conditions included Breast cancer (Patient had breast cancer for 10 years, which recurred in her left breast in August 2021. Patient had 10 lymph nodes removed from her left breast and left shoulder. Patient also had radiation treatment in January 2022, which resolved the second recurrence of her breast cancer. Patient is on exemestane 25mg PO daily.). Concomitant products included EXEMESTANE for Breast cancer.   In 2021, the patient received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. In 2021, received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. In 2021, the patient experienced PAIN IN EXTREMITY (sore right arm for 2 days after her second dose). In August 2021, the patient experienced BREAST CANCER RECURRENT (patient first had breast cancer 10 years ago/The breast cancer returned in August 2021 to her left breast) (seriousness criterion medically significant). The patient was treated with Radiotherapy (had a radiation treatment in Jan-2022 which had resolved second case of breast cancer) for Breast cancer recurrent. In 2021, PAIN IN EXTREMITY (sore right arm for 2 days after her second dose) had resolved. In January 2022, BREAST CANCER RECURRENT (patient first had breast cancer 10 years ago/The breast cancer returned in August 2021 to her left breast) had resolved.            The patient's breast cancer returned in Aug-2021 to her left breast. The patient had 10 lymph nodes removed from her left breast and left shoulder. She had a radiation treatment in Jan-2022 which had resolved second case of breast cancer.  Company Comment: This spontaneous case concerns a 78-year-old, female patient, with a history of breast cancer 10 years ago, who experienced an unexpected, medically significant serious event of Breast cancer recurrent approximately 6-7 months after vaccination with her 1st dose of mRNA-1273 vaccine. Patient was reportedly vaccinated with a 2nd dose of mRNA-1273 vaccine within 35 days after her 1st vaccination; subsequently, she received a booster dose with mRNA-1273 as well. On an unspecified date post-vaccination with her 1st dose, cancer recurred in her left breast that prompted lymphadenectomy of 10 lymph nodes from her left breast and left shoulder. Approximately 5 months after recurrence of her breast cancer, radiation treatment was started which reportedly resolved the second case of breast cancer. Her medical history of previous breast cancer remains as a confounder to the event Breast cancer recurrent. The benefit-risk relationship of mRNA-1273 is not affected by this report. Event's seriousness assessed based on medical judgement and the available information.   This case was linked to MOD-2022-542717 (Patient Link).; Sender's Comments: This spontaneous case concerns a 78-year-old, female patient, with a history of breast cancer 10 years ago, who experienced an unexpected, medically significant serious event of Breast cancer recurrent approximately 6-7 months after vaccination with her 1st dose of mRNA-1273 vaccine. Patient was reportedly vaccinated with a 2nd dose of mRNA-1273 vaccine within 35 days after her 1st vaccination; subsequently, she received a booster dose with mRNA-1273 as well. On an unspecified date post-vaccination with her 1st dose, cancer recurred in her left breast that prompted lymphadenectomy of 10 lymph nodes from her left breast and left shoulder. Approximately 5 months after recurrence of her breast cancer, radiation treatment was started which reportedly resolved the second case of breast cancer. Her medical history of previous breast cancer remains as a confounder to the event Breast cancer recurrent. The benefit-risk relationship of mRNA-1273 is not affected by this report. Event's seriousness assessed based on medical judgement and the available information.