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Ipsilateral axillary adenopathy post-COVID mRNA vaccine has been widely reported and guidelines for management have been established. Isolated changes of axillary tail trabecular thickening without associated adenopathy in the breast present a diagnostic dilemma and no official guidelines have thus far been reported. This finding has been reported after COVID mRNA vaccine and has never been reported with any other vaccine. We report on a patient with such changes on screening mammography 1.5 months after the fifth dose of a COVID-mRNA vaccine and 1 week after RSV vaccine. This raises the possibility that such changes can be seen with vaccines other than the COVID mRNA series of vaccines. The main differential diagnosis includes mastitis and inflammatory breast cancer. The transient nature of this finding with spontaneous resolution at diagnostic mammography and the vaccination history helps to establish the diagnosis and exclude breast cancer.

Axillary lymphadenopathy has been reported after ipsilateral COVID-19 vaccination and can cause confusion for possible malignancy [1]. Intrinsic findings isolated to the breast has not been previously reported. This is the first case series of ipsilateral reversible changes of diffuse axillary tail trabecular thickening on screening mammography in totally asymptomatic patients in connection with COVID vaccination, 3 of which were isolated findings, confirmed by complete resolution of all imaging findings on follow up. In all instances, imaging was performed within 1 week of the first or third dose of an mRNA COVID-19 vaccine. These findings can be confused with breast cancer. Spontaneous resolution distinguishes vaccine-related findings from breast cancer.