An increase in the median progression-free survival when using cyclin-dependent kinase 4/6 inhibitors in combination with aromatase inhibitors led to high expectations from the analysis of the overall survival of patients with HR+/HER2- metastatic breast cancer. Of the three drugs in the group, the final data were obtained in the MONALEESA-2 and PALOMA-2 studies, while a statistically significant difference in median overall survival was achieved only with the use of ribociclib. The review discusses possible factors that could affect the final results of the presented studies. The effect of ribociclib on the value of OS in clinically unfavorable prognostic subgroups (for example, patients with visceral metastases) and on progression-free survival depending on the expression of molecular genetic factors that worsen patient survival (such as Rb, p16, Ki-67, CDKN2A, CCND1, ESR1) was analyzed.The combination of ribociclib and aromatase inhibitors has proven to be an advantage in the treatment of patients with HR+/HER2- metastatic breast cancer in terms of increasing both progression-free survival and overall survival. Efficacy has been proven in subgroups with clinical and molecular adverse prognostic factors.

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Background. There is a wide spectrum of metabolic and toxic disorders that can cause acute encephalopathy in cancer patients. In routine clinical practice, hypoglycemia, vitamin B1 (thiamine) deficit, fulminant liver failure, uremia, severe hypoand hypernatremia should be primarily excluded. Central neurotoxicity associated with hyperammonemia in patients receiving 5-fluorouracil (5-FU) and oral fluoropyrimidines should be considered in differential diagnosis. In this case, the analysis of the blood acid-base status and the detection of B-type hyperlactatemia can facilitate the diagnosis of the cause of encephalopathy.Case description. We present two cases of hyperlactatemia and encephalopathy in stage IV cancer patients with continuous infusion of 5-FU via a portable infusion pump.Conclusion. Diagnosis of the frequent fluoropyrimidin-related adverse effects, such as myelosuppression, anorexia, diarrhea, mucositis, and palm-plantar syndrome, are routine and mastered by an oncologist at the very beginning of his/her professional activity. Specific fluoropyrimidinerelated encephalopathy or hyperlactatemia are difficult to suspect and recognize. We hope our description will be useful to prevent possible diagnostic errors.