Grade 3, stage IIIA undifferentiated, pleomorphic high-grade sarcoma at the injection site; This literature-non-study case was reported in a literature article and describes the occurrence of MALIGNANT FIBROUS HISTIOCYTOMA (Grade 3, stage IIIA undifferentiated, pleomorphic high-grade sarcoma at the injection site) in a 73-year-old female patient who received mRNA-1273 (Spikevax) for COVID-19 prophylaxis.   LITERATURE REFERENCE:      The patient's past medical history included Kidney angiomyolipoma and Tumor resection (Renal angiomyolipoma status post resection in 2019) in 2019. Concurrent medical conditions included Hypertension and Hyperlipidemia.  On an unknown date, the patient received second dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. On an unknown date, the patient experienced MALIGNANT FIBROUS HISTIOCYTOMA (Grade 3, stage IIIA undifferentiated, pleomorphic high-grade sarcoma at the injection site) (seriousness criterion medically significant). The patient was treated with Surgery (Resection of the mass) for Malignant fibrous histiocytoma. At the time of the report, MALIGNANT FIBROUS HISTIOCYTOMA (Grade 3, stage IIIA undifferentiated, pleomorphic high-grade sarcoma at the injection site) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Diagnostic aspiration: revealed pathologic characteristics indicative of high-grade sarcoma. On an unknown date, Magnetic resonance imaging: MRI with and without contrast revealed a 5.2 cm soft tissue mass overlying the triceps region with irregular features concerning for malignancy. On an unknown date, Physical examination: remarkable for a 6 cm, circular, mobile, soft mass present in the right upper arm.   For mRNA-1273 (Spikevax) (Unknown), the reporter did not provide any causality assessments.   Concomitant medications were not reported.  Patient presented with worsening right upper arm swelling for the past two weeks.  Patient noticed the swelling two to four days after receiving second dose of the Moderna vaccine within 1 cm from the prior injection site.  Patient ultimately had resection of the mass four months after the initial visit and was diagnosed as having grade 3, stage IIIA undifferentiated, pleomorphic high-grade sarcoma.  Authors concluded that, it was unclear whether there was a true association between the vaccines and malignancy or inflammatory response exacerbating underlying malignancy. This case highlights the necessity to investigate and be aware of such rare, adverse complications that may be associated with the novel COVID-19 vaccinations to guide physicians in their differential diagnosis.  Company comment: This literature non-study case concerns a 73 year old female patient with no relevant medical history, who experienced the unexpected serious (medically significant) event of Malignant fibrous histiocytoma, within days (unspecified) of receiving the second dose of mRNA-1273 vaccine. Patient presented with worsening right upper arm swelling for the past two weeks. She noticed the swelling two to four days after receiving her second dose of the Moderna vaccine within 1 cm from the prior injection site. Physical examination was remarkable for a 6 cm, circular, mobile, soft mass present in the right upper arm. MRI with and without contrast revealed a 5.2 cm soft tissue mass overlying the triceps region with irregular features concerning for malignancy. Fine needle aspiration revealed pathologic characteristics indicative of high-grade sarcoma. The patient ultimately had resection of the mass four months after the initial visit and was diagnosed as having grade 3, stage IIIA undifferentiated, pleomorphic high-grade sarcoma. Authors concluded that currently, it is unclear whether there is a true association between the vaccines and malignancy or inflammatory response exacerbating underlying malignancy. No information on details pertaining to previous dose was available in the report. Elderly age of the patient could be risk factor for the event. The benefit-risk relationship of mRNA-1273 is not affected by this report.; Sender's Comments: This literature non-study case concerns a 73 year old female patient with no relevant medical history, who experienced the unexpected serious (medically significant) event of Malignant fibrous histiocytoma, within days (unspecified) of receiving the second dose of mRNA-1273 vaccine. Patient presented with worsening right upper arm swelling for the past two weeks. She noticed the swelling two to four days after receiving her second dose of the Moderna vaccine within 1 cm from the prior injection site. Physical examination was remarkable for a 6 cm, circular, mobile, soft mass present in the right upper arm. MRI with and without contrast revealed a 5.2 cm soft tissue mass overlying the triceps region with irregular features concerning for malignancy. Fine needle aspiration revealed pathologic characteristics indicative of high-grade sarcoma. The patient ultimately had resection of the mass four months after the initial visit and was diagnosed as having grade 3, stage IIIA undifferentiated, pleomorphic high-grade sarcoma. Authors concluded that currently, it is unclear whether there is a true association between the vaccines and malignancy or inflammatory response exacerbating underlying malignancy. No information on details pertaining to previous dose was available in the report. Elderly age of the patient could be risk factor for the event. The benefit-risk relationship of mRNA-1273 is not affected by this report.