Abstract
BACKGROUND: The origin of collagen autoimmune diseases is not fully understood. Some studies postulate a mechanism of molecular mimicry or heterologous immunity following viral infections triggering autoimmunity. Apart from infections, other exogenous factors such as visible light or X-rays have been reported to incite autoimmunity. CASE REPORT: We report a case of histologically and serologically confirmed subacute lupus erythematosus (SCLE) following radiotherapy for breast cancer. DISCUSSION: The close temporal and spatial correlation between radiotherapy and onset of SCLE in this patient suggests that an autoimmune reaction may have been triggered locally by functionally altering the immune system and breaking self-tolerance.