Objective: to evaluate the efficiency and toxicity to metronomic chemotherapy and to investigate factors of sensitivity to this kind of treatment.

Material and methods. The results of treatment of patients with metastatic colorectal cancer (mCRC) who were treated at Minsk City Clinical Oncologic Dispensary in 2016–2019 were analyzed (n = 140). Patients included in the main arm after the completion of standard therapy were prescribed metronomic maintenance chemotherapy, while patients in the control arm – dynamic observation only. Metronomic regimen consisted of oral capecitabine 500 mg 3 times a day and oral cyclophosphane 50 mg daily.

Results. The most common effect of metronomic maintenance chemotherapy is tumor stabilization (42.9 %). The use of metronomic maintenance chemotherapy in patients with mCRC can increase the median progression-free survival (PFS) from 7.4 to 9.1 months, and the median overall survival (OS) from 15.0 to 23.3 months (p < 0.001). The proposed treatment regimen is well tolerated by most patients; the toxicity of metronomic chemotherapy does not limit its duration. Metronomic maintenance chemotherapy is more effective in patients with low levels of CEA and CA 19–9 tumor markers. The median PFS in patients with CEA level below 2 upper limits of normal (ULN) was 10.6 months and 7.2 months at a marker level above this value (p <0.001). For groups of patients with CA 19–9 levels above and below 2 ULN, median PFS was 7.0 months and 10.3 months respectively (p <0.001). Patients with reduced levels of expression of the TS, DPD, Flt-1 genes have higher values of PFS (p = 0.0006, 0.0235 and 0.015, respectively) and OS (p = 0.0004, 0.041 and 0.0213, respectively). At the TS expression level below 6.3 rel. units risk of progression within 9 months decreases by 71 % (18 %, 148 %), with the TP level above 6.1 rel. units. – by 37 % (6 %, 75 %).

Conclusion. The use of metronomic maintenance chemotherapy increases the effectiveness of treatment of patients with mCRC without significantly increasing toxicity. The optimal criteria for sensitivity to this method of treatment are the levels of tumor markers CEA and CA 19–9 below 2 ULN, the expression level of the TS gene below 6.3 relative units.

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