Objective  To explore variations in serum homocysteine (Hcy) and cystatin C (Cys-C) levels in patients with small cell lung cancer (SCLC) and determine the correlation between chemotherapy efficacy in patients with SCLC and Hcy and Cys-C levels.

  Methods  From January 2018 to December 2020, 67 patients with SCLC (observation group) and 60 normal healthy people (control group) who provided informed consent were enrolled. Twenty-six limited-stage patients and 41 extensive-stage patients in the observation group were treated with etoposide combined with platinum. Hcy and Cys-C levels were detected in the observation group before and after two cycles chemotherapy and in the control group.

  Results  The level of Hcy in the observation group was significantly higher than that in the control group (P<0.05), while there was no statistically significant difference in Cys-C between the observation group and the control group (P>0.05). And there was no significant difference in Hcy and Cys-C levels between limited-stage patients and extensive-stage patients (P>0.05). Compared with control group, the Hcy levels in limited-stage patients and extensive-stage patients were significantly increased (P<0.05), while the Cys-C levels were not statistically significant (P>0.05). In the effective group, he levels of Hcy and Cys-C decreased significantly after chemotherapy compared with before chemotherapy (P<0.05). In the ineffective group, the levels of Hcy and Cys-C showed no statistically significant differences after chemotherapy compared with before chemotherapy (P>0.05).

  Conclusions  Hcy is positively correlated with the occurrence of SCLC. The combined detection of Hcy and Cys-C levels in the serum can help evaluate chemotherapy efficacy and observe dynamic changes in patients with SCLC.