This document provides methods and materials involved in assessing samples (eg, cancer cells) for the presence of homologous recombination deficiency (HRD) or HRD signature. For example, methods and materials are provided for determining whether a cell (eg, a cancer cell) contains an HRD signature. Materials and methods for identifying cells (eg, cancer cells) that are deficient in homologous recombination repair (HDR), and materials for identifying cancer patients who are likely to respond to a particular cancer treatment regimen and A method is also provided.