Dr Mitsudomi on Managing Uncommon EGFR Mutations Compared With Classical Exon 19/21 Alterations in NSCLC

“[An] uncommon mutation is not a homogeneous population. Some are relatively sensitive [to EGFR tyrosine kinase inhibitors], some are not very sensitive, [and] some are not oncogenic [themselves].”

Tetsuya Mitsudomi, MD, PhD, professor of surgery, vice director, and chief of the Division of Thoracic Surgery in the Department of Surgery at Kindai University Faculty of Medicine, discussed how uncommon EGFR mutations are classified and treated relative to the classical exon 19 deletion and exon 21 L858R mutations in EGFR-mutant non–small cell lung cancer (NSCLC), and why this heterogeneous population poses distinct treatment challenges.

According to Mitsudomi, the exon 19 deletion and the exon 21 L858R point mutation are considered the classical, or common, EGFR mutations, and though the exact definition of an uncommon mutation involves some ambiguity, EGFR alterations other than exon 19 deletions, L858R, and exon 20 insertions are generally classified as uncommon. He noted that this uncommon category is not a homogeneous group; it spans individual mutations with markedly different biological behavior, which complicates efforts to draw broad conclusions about the population as a whole.

Mitsudomi said uncommon EGFR mutations are typically not very sensitive to first-generation EGFR TKIs, but evidence shows relative sensitivity to second-generation TKIs, particularly afatinib (Gilotrif). Still, he noted that response rates with afatinib in this population do not match those achieved with third-generation TKIs in patients with classical mutations, underscoring a gap in the current treatment paradigm.

Mitsudomi concluded that because uncommon EGFR mutations vary so widely in their sensitivity to targeted therapy, and because some mutations are not even oncogenic on their own, treatment increasingly needs to be individualized according to the specific mutation identified, rather than managed under a single uncommon-mutation category. He said this heterogeneity underscores the need to develop new, more effective treatment options specifically for patients with uncommon EGFR mutations.