Although, in the current study, no prognostic evaluation was conducted owing to the short observation period and the small populations of TNBC and HER2-positive breast cancer, our observation of higher serum levels of sCD155 in patients with ER-negative and high Ki-67 breast cancers suggests that high levels of sCD155 in the serum might be useful for predicting poor prognosis in patients with breast cancer. Here, MKI67 is linked to breast cancer.