Human
epidermal growth factor receptor-positive
breast cancer is an aggressive
cancer which represents approximately a quarter of all breast
cancers worldwide. Recent advances have led to the development of targeted
therapies, such as
trastuzumab (H), which have significantly improved prognosis. Such
therapies are currently used alongside other chemotherapeutic agents, such as
paclitaxel (P) and
gemcitabine (G). The most common side effects of PGH combination
therapy include
thrombocytopenia and
anemias. However, there have been no previous reports of
myositis resulting from this combination. We report the case of a 54-year-old metastatic
breast cancer patient on PGH
therapy who developed
muscle weakness. The patient was initially treated with
trastuzumab,
pertuzumab, and
paclitaxel. However,
pertuzumab was changed to
gemcitabine due to severe
diarrhea. After the fourth cycle of PGH, the patient presented with
muscle weakness and
creatine kinase levels of up to 6755 U/L. Magnetic resonance imaging of the femur and pelvis revealed diffuse bilateral
myositis, suggesting a diagnosis of
gemcitabine-induced
myositis. The patient was placed on intravenous fluids and
corticosteroids, which resolved her condition. To our knowledge, this is the first report of
gemcitabine-induced
myositis in a
breast cancer patient. Further studies are needed to determine the underlying mechanisms of
gemcitabine-induced
myositis and develop preventative measures.