Objective To analyze the normal expression levels of different lung cancer tumor markers (TM) in the cerebrospinal fluid and to explore the influence of serum TM levels and brain parenchymal metastasis, to more accurately determine whether the cerebrospinal fluid TM levels of patients with suspected meningeal metastasis is elevated.

Methods The clinical data of 80 patients diagnosed with non-leptomeningeal metastasis at Tianjin Medical University Cancer Hospital between January 2015 and February 2024 were collected, including 16 patients without lung cancer and 64 patients with lung cancer. Normal TM levels in the cerebrospinal fluid of patients without lung cancer and the difference in TM levels between the cerebrospinal fluid and serum samples were analyzed. The correlation between serum and cerebrospinal fluid TM levels was also analyzed. We then compared the differences in TM levels in the cerebrospinal fluid between groups with brain parenchymal metastasis and without brain parenchymal metastasis.

Results Normal levels of TPSA, CA19-9, CEA, Cyfra21-1, and SCC in the cerebrospinal fluid were lower than those in the serum (P<0.05); however, the levels of ProGRP and NSE in the cerebrospinal fluid were higher than those in the serum (P<0.05). The levels of TPSA, SCC, ProGRP, NSE, CEA, CA19-9, and Cyfra21-1 in the cerebrospinal fluid did not correlate with those in the serum (all P>0.05). The cerebrospinal fluid levels of TPSA, SCC, ProGRP, and CA19-9 were not significantly increased in patients with brain parenchymal metastasis compared to those in patients without brain parenchymal metastasis (P>0.05). Although CEA and Cyfra21-1 levels increased (P<0.05), their median values increased by less than 2 times and were all within the reference range; whereas, the level of NSE in the group with brain parenchymal metastasis was lower than that in the control group.

Conclusions The basal levels of ProGRP and NSE in normal cerebrospinal fluid were significantly higher than those in the serum; whereas, the expression levels of other TM in the cerebrospinal fluid were significantly lower than those in the serum. Whether the levels of TM in the serum were elevated and whether brain parenchymal metastasis was present, did not have a clinically significant impact on the TM levels in the cerebrospinal fluid.