A Novel Somatic Point Mutation of the RET Proto‐oncogene in Tumor Tissues of Small Cell Lung Cancer Patients

We examined whether the novel point mutation from GCC (Ala) to GAC (Asp) at codon 664 in exon 11 of RET proto‐oncogene, which we had found in two small cell lung carcinoma (SCLC) cell lines, existed in genomic DNA of tumor tissues of the two SCLC patients from whom these SCLC cell lines were derived. Sequence analysis revealed that point mutation identical to that of the SCLC cell lines was present in amplified alleles of single‐strand conformational variants in genomic DNA of the tumor tissues, whereas it was not detected in genomic DNA of non‐tumor tissues of the patients. These results indicate that this mutation had initially occurred in the SCLC patients and was of somatic origin.