The primary challenges include the lower prevalence, the fluctuating dynamics of expression, the lack of diagnostic kits and specific antibodies, the heterogeneity of this biomarker’s expression in the context of SCLC, difficulty of obtaining suitable samples, as well as the lack of clear evidence of a correlation between PD-L1 expression and a greater effect of immunotherapeutic procedures. The gene discussed is CD274; the disease is small cell lung carcinoma.