CEACAM5 and neoplasm: Carcinoembryonic antigen levels rapidly decreased (Fig 2A), and spiral CT imaging on day 147 demonstrated a partial response by using RECIST version 1.1 (RECIST 1.1) (overall tumor reduction −30%), with a reduction in multiple right breast masses, axillary, neck and mediastinal lymphadenopathy, and left lung metastases; follow-up CT scan repeated on day 231 revealed a complete tumor response by using RECIST 1.1 (Fig 2D).