First-Line Treatment of Driver-Negative Non-Small Cell Lung Cancer

Immunotherapy-based regimens are an established standard of care for the first-line treatment of driver-negative (EGFR/ALK/ROS WT) advanced non-small cell lung cancer. With multiple immune-based regimens approved in the first-line setting, clinicians are faced in practice with a variety of treatment choices. This article summarizes the most up-to-date trial data on treatments for driver-negative advanced non-small cell lung cancer, including immunotherapy monotherapy, chemoimmunotherapy, and combination immunotherapy, providing a framework for clinicians based on PD-L1 and smoking status. A multibiomarker assay that may best predict immunotherapy response remains an active area of research.

Identification of Germline Mutations in East-Asian Young Never-Smokers with Lung Adenocarcinoma by Whole-Exome Sequencing

Recently, an increasing number of young never-smokers are diagnosed with lung cancer. The aim of this study is to investigate the genetic predisposition of lung cancer in these patients and discover candidate pathogenic variants for lung adenocarcinoma in young never-smokers. Peripheral blood was collected from 123 never-smoking east-Asian patients diagnosed with lung adenocarcinoma before the age of 40. Whole-exome sequencing (WES) was conducted on genomic DNA extracted from peripheral blood cells. As a result, 3,481 single nucleotide variants were identified. By bioinformatical tools and the published gene list associated with genetic predisposition of cancer, pathogenic variants were detected in ten germline genes: ATR, FANCD2, FANCE, GATA2, HFE, MSH2, PDGFRA, PMS2, SDHB, and WAS. Patients with pathogenic variants were more likely to occur in females (9/10, 90.0%) and have stage IV lung adenocarcinoma (4/10, 40%). Furthermore, germline mutations in 17 genes (ASB18, B3GALT5, CLEC4F, COL6A6, CYP4B1, C6orf132, EXO1, GATA4, HCK, KCP, NPHP4, PIGX, PPIL2, PPP1R3G, RRBP1, SALL4, and TTC28), which occurred in at least two patients, displayed potentially pathogenic effects. Gene ontology analysis further showed that these genes with germline mutations were mainly located in nucleoplasm and associated with DNA repair-related biological processes. The study provides spectrum of pathogenic variants and functional explanation for genetic predisposition of lung adenocarcinoma in young never-smokers, which sheds a light on prevention and early diagnosis of lung cancer.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43657-022-00062-1.

Comprehensive genomic profiling of Finnish lung adenocarcinoma cohort reveals high clinical actionability and SMARCA4 altered tumors with variable histology and poor prognosis

INTRODUCTION

Lung adenocarcinoma is the most common type of lung cancer and typically carries a high number of mutations. However, the genetic background of the tumors varies according to patients' ethnic background and smoking status. Little data is available on the mutational landscape and the frequency of actionable genomic alterations in lung adenocarcinoma in the Finnish population.

MATERIALS AND METHODS

We evaluated the gene alteration frequencies of 135 stage I-IV lung adenocarcinomas operated at Turku University Hospital between 2004 and 2017 with a large commercial comprehensive genomic profiling panel. Additionally, we correlated the alterations in selected genes with disease outcomes in 115 stage I-III patients with comprehensive follow-up data. The genomic alterations in a sub-cohort of 30 never-smokers were assessed separately.

RESULTS

Seventy percent of patients in the overall cohort and 77% in the never-smoker sub-cohort harbored an alteration or a genomic signature targetable by FDA and/or EMA approved drug for non-small cell carcinoma, respectively. In multivariable analysis for disease-specific survival, any alteration in SMARCA4 (DSS; HR 3.911, 95%CI 1.561-9.795, P=0.004) exhibited independent prognostic significance along with stage, tumor mutation burden, and predominant histological subtypes.

CONCLUSIONS

Over two thirds of our overall cohort, and especially never-smokers had an actionable genomic alteration or signature. SMARCA4 alterations, detected in 7.4% of the tumors, independently predicted a shortened overall and disease-specific survival regardless of the alteration type. Most SMARCA4 alterations in our cohort were missense mutations associated with differentiated predominant histological subtypes and immunohistochemical SMARCA4/BRG1 and TTF-1 positive status.

Somatic profile in lung cancers is associated to reproductive factors in never-smokers women: Results from the IFCT-1002 BioCAST study

BACKGROUND

Lung cancer in women is on the rise, with a higher proportion occurring in lifelong never-smokers. Lung cancer in never-smokers (LCINS) exhibits a high frequency of driver oncogene alterations. In this study, we aimed to investigate whether exposure to reproductive factors in women with LCINS may modulate the molecular pattern.

METHODS

All newly diagnosed LCINSs were included in a prospective, observational study (IFCT-1002 BioCAST). Each patient responded to a questionnaire including reproductive factors. Biomarker test results were also collected.

RESULTS

Two hundred and sixty women were included in this analysis, and 166 alterations were characterized. EGFR mutation frequency proved greater among patients with late menarche (74% in age>14 vs. 40% and 41% for 12-14 and ≤12 years, respectively; P=0.020) and tended to decrease with increasingly late age at menopause. In multivariate analysis, EGFR mutation frequency increased by 23% per increment of 1 year of age at menarche (P=0.048), and by 9% for each year at age at first birth (P=0.035). ALK alteration frequency was greater in women with high parity (50% in≥5 vs. 12% and 7% for 1-4 and nulliparity, respectively; P=0.021).

CONCLUSION

In a cohort of women LCINSs, female hormonal factors appear to impact molecular pattern.

Lung cancer in never smokers: The role of different risk factors other than tobacco smoking

Lung cancer (LC), the leading cause of cancer-related deaths worldwide, is a complex and highly heterogeneous disease. Additional to its biological complexity, LC patients are often confronted with a high degree of stigma, mostly from the association of the disease with tobacco. Nonetheless, a proportion of LC patients are never-smokers, a population which we are beginning to comprehensively explore. Several risk factors have been linked to LC in never-smokers. Studies have consistently shown that radon exposure and domestic fuel smoke increase LC risk. Additionally, infections such as Mycobacterium tuberculosis, and Human Papilloma Virus are also risk factors. Other less conclusive associations include inflammatory diseases such as asthma and sarcoidosis. Moreover, we are now aware that molecular characteristics of LC vary widely according to smoking history, with important therapeutic implications. This review comprehensively assesses the current knowledge in terms of risk factors and disease characteristics in the never-smoker lung cancer population.

Role of Low-Dose Computerized Tomography in Lung Cancer Screening among Never-Smokers

INTRODUCTION

The incidence of lung cancer among never-smokers has been increasing rapidly. The U. S. National Lung Screening Trial and the NELSON trial showed that screening using low-dose computerized tomography (LDCT) effectively reduced lung cancer mortality among heavy smokers. However, its effectiveness in never-smokers has not been well investigated. This study investigated the role of LDCT in lung cancer screening among never-smokers.

METHODS

The study was designed as a single-center, retrospective cohort study. We analyzed the data on patients who underwent LDCT screening between May 2003 and June 2016. Nodules detected by computerized tomography were classified according to the Lung Imaging Reporting and Data System criteria. The detection rate and lung cancer outcomes (type of cancer, staging of lung cancer, and mortality) according to smoking history were determined.

RESULTS

Of the 28,807 enrolled patients, 12,176 were never-smokers; of these patients, 7744 (63.6%) were women and 1218 (10.0%) were found to have lung nodules. Overall, lung cancer was diagnosed in 55 never-smokers (0.45%). In contrast, lung cancer was diagnosed in 143 (0.86%) of the 16,631 ever-smokers. Of the never-smokers with lung cancer, 51 (92.7%) presented with stage I disease, and all patients had adenocarcinomas.

CONCLUSIONS

In the never-smoker population, LDCT screening helped to detect a significant number of lung cancers. Most of these lung cancers were detected at a very early stage. The positive results of the National Lung Screening Trial in the United States and the NELSON trial may have established the value of LDCT screening for heavy smokers, but future research should consider the value of using LDCT screening in the never-smoker population.

Change in lung function in never-smokers with nontuberculous mycobacterial lung disease: A retrospective study

Purpose

Never-smokers account for a large proportion of subjects in general population studies on nontuberculous mycobacteria lung disease (NTM-LD). However, the influence of NTM infection on the lung function of never-smokers has not yet been evaluated. The aim of this study was to determine how NTM-LD impairs the lung function in never-smokers, and whether there are an association between successful NTM-LD treatment in radiologic outcomes and improvement in lung function of never-smokers with NTM-LD or not.

Methods

We performed a retrospective study of patients (1) who have never smoked during their lifetime; (2) with at least two respiratory specimens from sputum, one bronchial washing sample, or one lung tissue that were culture positive for the same NTM species; and (3) who underwent at least two pulmonary function tests. We enrolled healthy never-smokers as the control group.

Results

In 22 never-smokers with NTM-LD, the median forced expiratory volume in 1 s (FEV₁) and forced vital capacity (FVC) at baseline was lower than those in 9 healthy never-smokers [1800 vs 2080 ml (p = 0.23) and 2230 vs 2620 ml (p = 0.06)], respectively. The median change in FEV₁ in never-smokers with NTM-LD was lower than that in healthy never-smokers [−70 vs 20 ml per year (p = 0.07), respectively]. On univariate analysis, baseline %-predicted FEV₁ in never-smokers with NTM-LD was associated with changes in FVC (p = 0.026) and FEV₁ (p = 0.013). Anti-NTM treatment was administered for at least 1 year in 19 patients (86.4%). The relationship between worsening chest CT findings and rapid progressive decline in both FVC (p = 0.66) and FEV₁ (p = 0.23) were not significant.

Conclusion

Never-smokers with NTM-LD showed lung function decline. There was no association between successful NTM-LD treatment in radiologic outcomes and improvement in lung function of never-smokers.

Paired Phase II Studies of Erlotinib/Bevacizumab for Advanced Bronchioloalveolar Carcinoma or Never Smokers With Advanced Non-Small-cell Lung Cancer: SWOG S0635 and S0636 Trials

BACKGROUND

Before mutation testing of the epidermal growth factor receptor (EGFR) gene was recognized as highly associated with the activity of EGFR tyrosine kinase inhibitors (TKIs), clinically defined patient populations with bronchioloalveolar carcinoma (BAC) and never smokers were identified as likely to benefit from EGFR TKIs. From preclinical and clinical data suggesting potentially improved efficacy with a combination of an EGFR TKI and the antiangiogenic agent bevacizumab, the Southwestern Oncology Group (SWOG) initiated paired phase II trials to evaluate the combination of erlotinib/bevacizumab in patients with advanced BAC (SWOG S0635) or never smokers with advanced lung adenocarcinoma (SWOG S0636).

MATERIALS AND METHODS

Eligible patients with BAC or adenocarcinoma with BAC features (SWOG S0635) or never smokers with advanced lung adenocarcinoma (SWOG S0636) received erlotinib 150 mg/day with bevacizumab 15 mg/kg until progression or prohibitive toxicity. Never smokers with BAC were preferentially enrolled to SWOG S0636. The primary endpoint for both trials was overall survival.

RESULTS

A total of 84 patients were enrolled in the SWOG S0635 trial and 85 in the SWOG S0636 trial. The objective response rate was 22% (3% complete response) in the SWOG S0635 trial and 50% (38% confirmed; 3% complete response) in the SWOG S0636 trial. The median progression-free survival was 5 and 7.4 months in the S0635 and S0636 trials, respectively. The median overall survival was 21 and 29.8 months, respectively. Toxicity consisted mainly of rash and diarrhea in both trials.

CONCLUSION

Although the field has moved toward molecular, rather than clinical, selection of patients as optimal candidates for EGFR TKI therapy, these results support the hypothesis that a subset of patients in whom erlotinib is particularly active could receive an incremental benefit from the addition of bevacizumab.

Establishment and characterization of an oral tongue squamous cell carcinoma cell line from a never-smoking patient

OBJECTIVE

The rising incidence of oral tongue squamous cell carcinoma (OTSCC) in patients who have never smoked and the paucity of knowledge of its biological behavior prompted us to develop a new cell line originating from a never-smoker.

MATERIALS AND METHODS

Fresh tumor tissue of keratinizing OTSCC was collected from a 44-year-old woman who had never smoked. Serum-free media with a low calcium concentration were used in cell culture, and a multifaceted approach was taken to verify and characterize the cell line, designated UCSF-OT-1109.

RESULTS

UCSF-OT-1109 was authenticated by STR DNA fingerprint analysis, presence of an epithelial marker EpCAM, absence of human papilloma virus (HPV) DNA, and SCC-specific microscopic appearance. Sphere-forming assays supported its tumorigenic potential. Spectral karyotype (SKY) analysis revealed numerical and structural chromosomal abnormalities. Whole-exome sequencing (WES) identified 46 non-synonymous and 13 synonymous somatic single-nucleotide polymorphisms (SNPs) and one frameshift deletion in the coding regions. Specifically, mutations of CDKN2A, TP53, SPTBN5, NOTCH2, and FAM136A were found in the databases. Copy number aberration (CNA) analysis revealed that the cell line loses chromosome 3p and 9p, but lacks amplification of 3q and 11q (as does HPV-negative, smoking-unrelated OTSCC). It also exhibits four distinctive focal amplifications in chromosome 19p, containing 131 genes without SNPs. Particularly, 52 genes showed >3- to 4-fold amplification and could be potential oncogenic drivers.

CONCLUSION

We have successfully established a novel OTSCC cell line from a never-smoking patient. UCSF-OT-1109 is potentially a robust experimental model of OTSCC in never-smokers.

Proportion and clinical features of never-smokers with non-small cell lung cancer

BACKGROUND

The proportion of never-smokers with non-small cell lung cancer (NSCLC) is increasing, but that in Korea has not been well addressed in a large population. We aimed to evaluate the proportion and clinical features of never-smokers with NSCLC in a large single institution.

METHODS

We analyzed clinical data of 1860 consecutive patients who were newly diagnosed with NSCLC between June 2011 and December 2014.

RESULTS

Of the 1860 NSCLC patients, 707 (38.0%) were never-smokers. The proportions of women (83.7% vs. 5.6%) and adenocarcinoma (89.8% vs. 44.9%) were higher among never-smokers than among ever-smokers. Significantly more never-smokers were diagnosed at a younger median age (65 vs. 68 years, P < 0.001) and earlier stage (stage I-II, 44.5% vs. 38.9%, P = 0.015) compared with ever-smokers. Epidermal growth factor receptor mutations (57.8% vs. 24.4%, P < 0.001) and anaplastic lymphoma kinase rearrangements (7.8% vs. 2.8%, P < 0.001) were more common in never-smokers, whereas Kirsten rat sarcoma viral oncogene homolog mutations (5.8% vs. 9.6%, P = 0.021) were less frequently encountered in never-smokers than in ever-smokers. Never-smokers showed longer survival after adjusting for the favorable effects of younger age, female sex, adenocarcinoma histology, better performance status, early stage disease, being asymptomatic at diagnosis, received antitumor treatment, and the presence of driver mutations (hazard ratio, 0.624; 95% confidence interval, 0.460-0.848; P = 0.003).

CONCLUSIONS

More than one-third of the Korean patients with NSCLC were never-smokers. NSCLC in never-smokers had different clinical characteristics and major driver mutations and resulted in longer overall survival compared with NSCLC in ever-smokers.

The Risk Factors and Characteristics of COPD Among Nonsmokers in Korea: An Analysis of KNHANES IV and V

PURPOSE

Chronic obstructive pulmonary disease (COPD) is increasing in prevalence and mortality. This study evaluated the prevalence, risk factors, characteristics, and health-related quality of life (HRQoL) of COPD among nonsmokers in Korea.

METHODS

This was a population-based cross-sectional study using data obtained from the Fourth and Fifth Korean National Health and Nutrition Examination Survey, which was conducted from 2007 to 2011.

RESULTS

A total of 15,063 participants completely answered the questionnaire and performed the spirometry. Among them, 59.6 % were nonsmokers and 40.4 % were smokers. The prevalence of nonsmoker COPD was 7.1 %. On multivariate analysis, age ≥65 years (OR, 2.93; 95 % CI, 2.44-3.51), male sex (OR, 2.98; 95 % CI, 2.40-3.71), living in rural area (OR, 1.26; 95 % CI, 1.05-1.51), lower body mass index (BMI) (<18.5 kg/m(2)) (OR, 3.00; 95 % CI, 1.78-5.01), self-reported asthma (OR, 2.72; 95 % CI, 2.05-3.60), and self-reported tuberculosis (OR, 4.73; 95 % CI, 3.63-6.17) showed a significantly higher risk of nonsmoker COPD. Analysis of nonsmoker and smoker COPD revealed that there are more females in nonsmoker COPD patients (73.9 vs. 6.9 %, P < 0.001). Nonsmoker COPD patients presented with impaired mobility, pain/discomfort, and anxiety/depression functions as well as a lower mean EuroQol Five-Dimension Questionnaire utility score, which showed HRQoL.

CONCLUSIONS

The burden of nonsmoker COPD was considerable. Older age, male sex, lower BMI, self-reported asthma, and self-reported tuberculosis were risk factors for nonsmoker COPD and there were differences between nonsmoker and smoker COPD in terms of sex, comorbidities, and HRQoL.

Small-cell lung cancer in never-smokers: A case series

Small-cell lung cancer (SCLC) is closely correlated with smoking and only sporadic cases have been reported in non-smoking patients. Environmental tobacco smoke and/or occupational risk factors have been suggested as possible causes of lung cancer in this subset of patients. However, particularly in relation to SCLC there is not enough reliable information. All patients with lung cancer in follow-up for a period of three-months at the Pulmonology Unit of Coimbra University Hospital were retrospectively assessed. From a total of 303 patients, 35 had SCLC, 4 of which were never-smokers and their clinical cases are hereby presented. A detailed questionnaire was given to all patients, which excluded second-hand smoking or occupational hazards. They were all female with a mean age of 63.0 ± 15.7 years. The most frequent complaints were cough, dyspnoea, anorexia and significant weight loss. Diagnosis was obtained by transbronchial biopsies in all cases. Two patients had locally advanced disease and the other two had extensive-disease due to distant metastases. Treatment approaches included first-line chemotherapy with platin and etoposide duplet and partial remission was achieved in half the cases. All patients died; mean survival was 15.8 ± 3.8 months. Further studies are needed for a better understanding of the pathogenicity of non-smoking related SCLC and we hope that this case series with its meticulous exclusion of potential risk factors will be a useful contribution.

Nicotine reinforcement in never-smokers

RATIONALE

Global tobacco-related mortality dwarfs that of all other drugs. Nicotine is believed to be the primary agent responsible for tobacco use and addiction. However, nicotine is a relatively weak and inconsistent reinforcer in nonhumans and nicotine reinforcement has not been demonstrated in never-smokers.

OBJECTIVES

This study investigated the discriminative, subjective, and reinforcing effects of nicotine in never-smokers.

METHODS

Eighteen never-smokers (< 50 lifetime nicotine exposures) participated in a double-blind study. During a drug discrimination phase, volunteers ingested oral nicotine and placebo capsules (quasi-random order) at least 2 h apart and rated subjective effects repeatedly for 2 h after ingestion in daily sessions. Blocks of 10 sessions were continued until significant discrimination was achieved (p ≤ 0.05, binomial test; ≥ 8 of 10). Following discrimination, nicotine choice was tested by having volunteers choose which capsule set to ingest on each daily session. Successive blocks of 10 sessions were conducted until choice for nicotine or placebo met significance within each volunteer (≥ 8 of 10 sessions).

RESULTS

All 18 volunteers significantly discriminated nicotine from placebo; the lowest dose discriminated ranged from 1.0 to 4.0 mg/70 kg. Nine volunteers significantly chose nicotine (choosers) and nine significantly chose placebo (nicotine avoiders). The choosers reported predominately positive nicotine subjective effects (e.g., alert/attentive, good effects, liking), while avoiders tended to report negative effects (e.g., dizzy, upset stomach, disliking). Both choosers and avoiders attributed their choice to the qualitative nature of drug effects.

CONCLUSIONS

These results provide the first evidence that nicotine can function as a reinforcer in some never-smokers.

A family history of cancer and lung cancer risk in never-smokers: A clinic-based case-control study

OBJECTIVE

Some population-based studies involving lung cancer patients have reported that inherited susceptibility is responsible for the familial aggregation observed in non-smoking lung cancer patients; however, it has been found that the false-negative rates in clinic-ascertained probands are significantly lower than population-ascertained probands. In this clinic-based study, we sought to determine the relationship between a family history of cancer and lung cancer risk in Chinese never-smokers.

METHODS

In this clinic-based case-control study, all 318 probands and 509 controls were Chinese. The data on demographic characteristics, age, gender, race, lung disease history, living environment, occupational exposure, and smoking history were collected from a structured questionnaire. Multiple conditional logistic regression was used to estimate adjusted odds ratios (aOR) and 95% CIs after adjusting for possible confounders.

RESULTS

The risk of lung cancer was increased in individuals with a family history of lung (aOR, 3.21; p<0.001) or any other cancer (aOR, 1.79; p<0.001). Analyses were carried out using stratified relative gender; first-degree female relatives tended to have a higher risk than first-degree male relatives. Similarly, the aOR for a female developing a malignant tumor was two times greater than controls.

CONCLUSIONS

Our analysis provides further evidence of the importance of genetic factors underlying lung cancer in patients who are never-smokers, especially in patients with a maternal history of cancer.

RARβ2 hypermethylation is associated with poor recurrence-free survival in never-smokers with adenocarcinoma of the lung

Background

This study was aimed at investigating if the effect of RARβ2 hypermethylation on recurrence-free survival (RFS) in non-small cell lung cancer (NSCLC) depends on one’s smoking status and specific interacting proteins.

Results

We retrospectively analyzed the expressions of five proteins using immunohistochemistry in archival formalin-fixed and paraffin-embedded tissues from 578 NSCLC patients who had undergone surgical resection from 1994 through 2004. Promoter methylation of RARβ2 was assessed by bisulfite pyrosequencing. Recurrence was found in 268 (46%) of 578 NSCLCs with a median follow-up period of 4.8 years. Overexpression of β-catenin, c-MET, cyclin D1, and EGFR occurred in 55%, 72%, 51%, and 41% of the patients, respectively. E-cadherin expression was negative in 62% of the patients, and RARβ2 hypermethylation was found in 37%. The abnormal expression of c-MET (P = 0.002) and EGFR (P = 0.001) was found to be highly prevalent in never-smokers. RARβ2 hypermethylation was significantly associated with poor recurrence-free survival (RFS) in 128 never-smokers with adenocarcinoma (P = 0.01) For parsimonious model building, the five proteins were clustered into three groups (β-catenin and E-cadherin; c-MET; cyclin D1 and EGFR) by an unsupervised hierarchical clustering and were included in a multivariate analysis. Cox proportional hazard analysis showed that RARβ2 hypermethylation was significantly associated with poor RFS in 128 never-smokers with adenocarcinoma (adjusted hazard ratio [HR] = 2.19, 95% confidence interval [CI] = 1.28 to 3.47; P = 0.009), after adjusting for interacting proteins.

Conclusions

The present study suggests that RARβ2 hypermethylation may be an independent prognostic factor of RFS in never-smokers with adenocarcinoma of the lung.

De novo pulmonary small cell carcinomas and large cell neuroendocrine carcinomas harboring EGFR mutations: Lack of response to EGFR inhibitors

INTRODUCTION

Epidermal growth factor receptor (EGFR) mutations are present in 10-20% of all non-small-cell lung cancers and predict for response to EGFR tyrosine kinase inhibitors (TKIs). However, the incidence of these mutations and their ability to predict response to TKIs in high-grade pulmonary neuroendocrine carcinomas [i.e. small cell lung cancer (SCLC) and large cell neuroendocrine carcinoma (LCNEC)] is unknown.

METHODS

The presence of EGFR mutations, clinicopathologic and anti-cancer therapy response data were retrospectively compiled and analyzed from a cohort of 608 patients-lung tumors to identify EGFR mutated high-grade pulmonary neuroendocrine carcinomas. We identified 126 EGFR-mutated (21.8% of 578 successful genotyped cases) lung cancers and only 2 (1.6%) were high-grade neuroendocrine carcinomas.

RESULTS

Case one was of a 63 year-old white never smoker woman with extensive stage SCLC harboring EGFR-delL747_P753insS but without EGFR protein expression. After progression on carboplatin/etoposide, the patient was treated with erlotinib and developed progressive disease with a survival <3 months from start of erlotinib. Case two was of a 73 year-old Asian 30 pack-year smoker man with metastatic LCNEC harboring EGFR-delL747_P753insQS and also lacking EGFR protein expression. The patient received first line therapy with erlotinib and had progressive disease with a survival of 4 months.

CONCLUSIONS

The lack of response to EGFR TKIs in EGFR mutated de novo SCLC and LCNEC reported here may indicate that tumor differentiation affects tumor dependency on EGFR as a driver oncogene.