PLLP and small cell lung carcinoma: The decreased expression of COLEC12 may suppress the host defense function and immune cell infiltration, thereby promoting the development of SCLC; The decreased expression of HP may inhibit the clearance pathway of free hemoglobin, leading to the enhancement of oxidative stress and inflammatory response, thereby promoting the development of SCLC; and the decreased expression of PLLP may promote the development of SCLC by influencing the neuroendocrine characteristics.