Overall, 73% of the cfDNA samples were classified as ASCL1, 13% were classified as NEUROD1 and 14% were classified as being double negative, with the distribution of the subtypes correlating closely to previously published immunohistochemistry data from SCLC tissue samples (Fig. 5f; chi-squared test, χ2 = 0.628, d.f. = 2, P = 0.73). Here, ASCL1 is linked to small cell lung carcinoma.