In Horizons in Cancer Research. Volume 73, after the identification of some small subgroups with a strong biological-molecular identity, the current evidence regarding the prognostic factors of patients with non-eradicable metastatic disease are examined. The goal is to discuss disease subgroups, which may sometimes provide conditions for decisions that are less compliant with current clinical practice and help define new stratification criteria for patients enrolled in prospective studies. Following this, the authors summarize the current knowledge on breast cancer with an introduction on the traditional markers used in the diagnosis of this disease, followed by an account of the emerging markers. Next, the underlying mechanisms of DNA replication, damage and repair are discussed. Further, RAD51 is proposed as a potential means of managing chemoresistant cancers. Certain drugs and strategies can sensitize chemotherapy via impacting on RAD51, which can be developed as chemotherapy modulators. The authors also discuss multiple myeloma, an incurable malignant tumor of plasma cells of the bone marrow, which is the most common primary neoplasm arising in bone. It causes approximately 1% of cancer-related deaths and is the 2nd most common hematological malignancy in the western world. Later, this collection discusses the prevalence and types of infectious complications that patients with multiple myeloma face, as well as present and emerging therapeutic approaches. The concluding study indicates proteins that have a promising future as new anticancer drugs, in conjunction with the in vitro and/or in vivo effects of these bioactive proteins derived from plants.