Regarding the molecular pathogenesis and driver mutations in non-small cell lung cancer (NSCLC), all of the following are correct EXCEPT:

Explanation

## Molecular Pathogenesis of NSCLC — Driver Mutations **Key Point:** While TP53 mutations are indeed very common in NSCLC (found in ~50–70% of cases), they are NOT the primary therapeutic target because TP53 is a tumor suppressor gene and loss-of-function mutations cannot be directly targeted with small molecules. The correct statement is that TP53 mutations are frequent but NOT the primary actionable driver. ### Common Actionable Driver Mutations in NSCLC | Mutation | Frequency | Histology Preference | Therapeutic Target | Clinical Significance | |----------|-----------|----------------------|-------------------|----------------------| | EGFR | 10–15% (Asian > Western) | Adenocarcinoma >> SCC | EGFR-TKIs (gefitinib, erlotinib, afatinib) | Excellent response; predictive of TKI sensitivity | | ALK | 3–5% | Adenocarcinoma | ALK inhibitors (crizotinib, alectinib, brigatinib) | Excellent response; younger patients | | KRAS | 25–30% | Adenocarcinoma > SCC | Historically untargetable; now KRAS G12C inhibitors (sotorasib) | Mutually exclusive with EGFR; poor prognosis | | TP53 | 50–70% | All types | NOT a direct therapeutic target (tumor suppressor) | Associated with aggressive behavior; poor prognosis | | ROS1 | 1–2% | Adenocarcinoma | ROS1 inhibitors (crizotinib, ceritinib) | Excellent response | **High-Yield:** EGFR, ALK, ROS1, and KRAS G12C are **actionable drivers** with specific targeted therapies. TP53 loss is a **passenger mutation** that indicates aggressive disease but is not directly targetable. **Clinical Pearl:** The distinction between "common" and "actionable" is critical: TP53 mutations are the most frequent but are loss-of-function alterations affecting tumor suppression, not gain-of-function oncogenic drivers. Patients with TP53 mutations benefit from conventional chemotherapy and immunotherapy, not targeted TKIs. **Warning:** Do not confuse frequency with therapeutic actionability. TP53 is frequent but not a therapeutic target; EGFR and ALK are less frequent but highly actionable. ### Why Option 3 Is Incorrect The statement claims TP53 mutations are found in >90% of NSCLCs and are the "primary therapeutic target." Both parts are wrong: 1. TP53 mutations occur in ~50–70% of NSCLCs, not >90%. 2. TP53 is NOT a primary therapeutic target because it is a tumor suppressor gene; loss of function cannot be reversed by small-molecule inhibitors. [cite:Robbins 10e Ch 15]