She had a spread of her breast cancer; she also had diarrhea after she got the Spikevax; This spontaneous case was reported by a nurse and describes the occurrence of BREAST CANCER METASTATIC (She had a spread of her breast cancer) in an elderly female patient who received mRNA-1273 (Moderna COVID-19 Vaccine) (batch nos. 031M20A, 006B21A, 037F21A and 017B22A) for COVID-19 prophylaxis. The occurrence of additional non-serious events is detailed below.     Concurrent medical conditions included Kidney stones (Taking some medications for, she had it for years before she got 1st dose of the Moderna vaccine.). Concomitant products included INFLUENZA VACCINE for an unknown indication.   On 24-Feb-2021, the patient received first dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 24-Mar-2021, received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 07-Sep-2021, received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 15-Jul-2022, received fourth dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On an unknown date, the patient experienced BREAST CANCER METASTATIC (She had a spread of her breast cancer) (seriousness criterion medically significant) and DIARRHOEA (she also had diarrhea after she got the Spikevax). At the time of the report, BREAST CANCER METASTATIC (She had a spread of her breast cancer) had not resolved and DIARRHOEA (she also had diarrhea after she got the Spikevax) had resolved.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Biopsy: tiny nodules on her chest. When they were big enough, they took a biopsy and it was found that she had a spread of her breast cancer.. On an unknown date, Computerised tomogram thorax: tiny nodules on her chest.. On an unknown date, Mammogram: found out it was breast cancer, it was a pretty big mass, 2.5 cm..     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter considered DIARRHOEA (she also had diarrhea after she got the Spikevax) to be related. No further causality assessment was provided for BREAST CANCER METASTATIC (She had a spread of her breast cancer).    Concomitant product also include unspecified drug for kidney stones. It was reported that She had flu vaccine 3 weeks before she got the Spikevax.  Patient receives fifth dose of moderna vaccine on 07-Oct-2022 (Lot number-027E22A) and sixth dose on 24-Oct-2023 (Lot number- 3031047).  It was reported that after she got the first dose of the Moderna vaccine, they found a lump on her right breast. They initially thought that it was a swollen lymphnode as it was towards her right armpit. But when they did a mammogram, they found out it was breast cancer and it was a pretty big mass, 2.5 cm. She had a mastectomy and the lymph nodes the took out did not have cancer. Based on the genetic testing they requested, she had chemotherapy and did not had radiation. She also had CT of the chest and they saw tiny nodules on her chest. When they were big enough, they took a biopsy and it was found that she had a spread of her breast cancer. But she was asymptomatic. she also had diarrhea after she got the Spikevax vaccine, but this might had been due to the chemo drug that she was taking. She only had one episode and it got resolved.  Company Comment This is a Spontaneous case reported by a nurse, concerning an elderly female patient, with no relevant medical history, who experienced the unexpected and serious (due to medically significant) event of Breast cancer metastatic, which occurred on an unknown date after the first dose of mRNA-1273 vaccine. As reported, after mRNA-1273 first dose, a lump on her right breast was found. Mammogram was performed and showed breast cancer (mass of 2.5 cm). She had a mastectomy and the lymph nodes that were taken out did not have cancer. Based on the genetic testing that was requested, she had chemotherapy and did not have radiation. She also had CT of the chest and they saw tiny nodules on her chest. Biopsy revealed that she had a spread of her breast cancer. But she was asymptomatic. At the time of the report, the event had not resolved. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.