Abstract: In alternative embodiments, provided are immunohistochemistry (IHC) methods for determining and scoring reproducibly the extent of expression of the protein carcinoembryonic antigen-related cell adhesion molecule 5, or CEACAM5, in a tissue sample. In alternative embodiments, provided are methods for diagnosing, treating or ameliorating or assessing the risk of recurrence for a cancer or a tumor using an IHC method as provided herein. In alternative embodiments, provided are kits comprising components and instructions for practicing methods as provided herein. The present application describes methods for scoring CEACAM5 expression and utilizing the score as a companion or complementary diagnostic or to treat or ameliorate cancer or a tumor.