Overview

The 73-gene lung cancer genetic testing panel is a next-generation sequencing assay designed to interrogate seventy-three genes relevant to the diagnosis, treatment selection, and progression of non-small cell lung cancer. The panel covers driver mutations such as EGFR, KRAS, BRAF, MET and HER2, resistance-associated alterations, and genes that inform immunotherapy decisions such as STK11, KEAP1 and tumour mutational burden markers.

In routine clinical practice, the panel is used at multiple decision points. It is used at diagnosis to identify the driver alteration that determines first-line therapy. It is used during treatment to confirm molecular progression. And, most relevant here, it is used at the time of progression on a targeted first-line regimen to map the resistance landscape and guide the next line of therapy.

What Resistance Looks Like After First-Line EGFR Therapy

Per NCCN and ESMO guidelines for non-small cell lung cancer, the standard first-line option for EGFR-mutant disease is a third-generation EGFR tyrosine kinase inhibitor. The median duration of response is typically measured in months, after which most patients progress. Progression is rarely random; it follows recognisable molecular patterns that the 73-gene panel is designed to detect.

The most common on-target resistance mechanism is the acquisition of a secondary EGFR mutation such as T790M after first- or second-generation EGFR TKI therapy, or the emergence of tertiary mutations after osimertinib. Off-target resistance is also frequent. MET amplification, HER2 amplification, transformation to small-cell histology, and bypass-track activation through KRAS or PI3K pathway alterations are all observed in real-world cohorts. Each of these resistance mechanisms points to a distinct next-line strategy, ranging from a switch in TKI to combination regimens, chemotherapy, or trial enrolment.

The 73-gene panel is well suited to detecting these alterations in a single assay. It interrogates EGFR across its full coding sequence, captures MET and HER2 copy-number changes, and reports gene fusions and other structural variants when present. The panel can be performed on tissue at progression or on circulating tumour DNA when tissue is not accessible.

From Result to Next-Line Decision

The clinical report from a 73-gene panel at progression should be integrated with the patient's treatment history and current performance status. Per NCCN, the choice of next-line therapy depends on the specific resistance mechanism identified, the pace of progression, and the patient's tolerance of the prior regimen. The panel result is necessary but not sufficient; clinical context completes the picture.

A molecular tumour board or a multidisciplinary lung cancer team often reviews the report before the next-line decision is finalised, particularly when an unusual resistance pattern is identified or when a clinical trial is being considered.

FAQ

Q: Does this panel predict who will develop resistance? A: It maps resistance once it has emerged. It is run at progression, not as a routine surveillance test on a stable patient.

Q: Can a 73-gene panel be done on blood rather than tissue? A: Yes. Liquid biopsy NGS panels are validated for many of the same alterations and are useful when tissue is not available at progression.

Q: Is MET amplification the most common off-target resistance? A: Per major resistance reviews, MET amplification is one of the most frequent off-target mechanisms after EGFR TKI therapy, alongside HER2 amplification and small-cell transformation.

Q: How quickly should the panel be ordered at progression? A: Per NCCN, molecular profiling at progression is recommended so that next-line therapy can be planned without delay.