EGFR and Nasal polyposis: To examine the impact of EGFR exon 20 insertion mutations on SIP development, we transduced immortalized nasal polyp cell line, iNP2, with recombinant retroviral vectors carrying EGFR exon 20 insertion mutants, ERBB1_S768_D770dup or ERBB1_N771_H773dup, as well as a typical exon 19 deletion mutant, ERBB1_E746_A750del to generate iNP2_S768_D770dup, iNP2_N771_H773dup, and iNP2_E746_A750del cells.