The present disclosure provides rapid and non-invasive methods for determining whether a patient exhibiting cancer symptoms, or at risk for hereditary cancers such as breast cancer, ovarian cancer, colon cancer, or skin cancer, will benefit from treatment with one or more therapeutic agents. These methods are based on detecting hereditary cancer-related mutations in small-volume dried biological fluid samples that are collected using a volumetric absorptive microsampling device (e.g., MITRA Tip). Kits for use in practicing the methods are also provided.