Rare molecular subtypes of lung cancer

Oncogenes that occur in ≤5% of non-small-cell lung cancers have been defined as ‘rare’; nonetheless, this frequency can correspond to a substantial number of patients diagnosed annually. Within rare oncogenes, less commonly identified alterations (such as HRAS, NRAS, RIT1, ARAF, RAF1 and MAP2K1 mutations, or ERBB family, LTK and RASGRF1 fusions) can share certain structural or oncogenic features with more commonly recognized alterations (such as KRAS, BRAF, MET and ERBB family mutations, or ALK, RET and ROS1 fusions). Over the past 5 years, a surge in the identification of rare-oncogene-driven lung cancers has challenged the boundaries of traditional clinical grade diagnostic assays and profiling algorithms. In tandem, the number of approved targeted therapies for patients with rare molecular subtypes of lung cancer has risen dramatically. Rational drug design has iteratively improved the quality of small-molecule therapeutic agents and introduced a wave of antibody-based therapeutics, expanding the list of actionable de novo and resistance alterations in lung cancer. Getting additional molecularly tailored therapeutics approved for rare-oncogene-driven lung cancers in a larger range of countries will require ongoing stakeholder cooperation. Patient advocates, health-care agencies, investigators and companies with an interest in diagnostics, therapeutics and real-world evidence have already taken steps to surmount the challenges associated with research into low-frequency drivers. Lung cancers harbouring ‘rare’ alterations (defined as those with a prevalence of <5% of oncogene-driven lung cancers) can be detected in around a third of all oncogene-driven lung cancers and are diagnosed in thousands of patients each year. Advances in our understanding of tumour biology, diagnosis and the development of novel therapies are enabling increasing use of specific therapies targeting these alterations. In this Review, the authors provide an overview of the epidemiology, diagnosis, prognosis and treatment of patients with lung cancers harbouring these rare alterations. The importance of expedited drug approval pathways and cooperation between multiple stakeholders is also emphasized.