Primary chemoradiation with cisplatin versus cetuximab for locally advanced head and neck cancer: a retrospective cohort study

Objective To explore the efficacy of primary chemoradiation with cisplatin versus cetuximab with respect to HPV/p16 and smoking statuses. Methods We retrospectively reviewed patients from our center with locally advanced non-nasopharyngeal head and neck squamous cell carcinoma (HNSCC) who received primary chemoradiation with cisplatin or cetuximab between 2006 and 2018. Results The median OS for cisplatin (n = 66) was not reached versus 132 months when treated with cetuximab (n = 55) (p = 0.03). For HPV/p16-positive patients, we found the median OS for cisplatin (n = 34) was not reached versus 60 months with cetuximab (n = 21) (p = 0.036). In the smoking group, the median OS was not reached in the cisplatin group (n = 44) versus 60 months when treated with cetuximab (n = 32) (p = 0.03). Conclusion HPV/p16-positive and smoking cohorts treated with cisplatin-based chemoradiotherapy had a significantly better OS versus cetuximab.


Background
Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer in the world, with 650,000 new cases diagnosed each year. Tobacco use, heavy alcohol intake, and carcinogenic human papillomavirus (HPV) are strong risk factors [1,2]. HPV-positive HNSCC responds favorably to chemoradiation leading to improved prognosis [3,4].
Patients who have locoregionally advanced disease at diagnosis receive combined modality therapy with a platinum-based chemotherapy backbone; [5,6] however, in 2006, cetuximab, a chimeric monoclonal antibody and an epidermal growth factor receptor (EGFR) inhibitor, was approved with radiation therapy for locoregionally advanced HNSCC. The addition of cetuximab to radiotherapy improved survival in HNSCC [7]. Cetuximab has been proposed as an alternative to platinum chemotherapy due to a more favorable toxicity profile and improved tolerability in those with renal disease or in the elderly. However, two recent multi-centers randomized clinical trials in patients with HPV associated HNSCC have demonstrated both inferior overall survival of patients who received cetuximab based instead of cisplatin-based radiotherapy and no difference in terms of toxicity profile [8,9]. One hypothesis for the decreased efficacy of cetuximab in HPV associated HNSCC is the decreased dependence on the EGFR pathway compared to HPVnegative tumors [10]. We aimed to compare real-world outcomes of cisplatin-based versus cetuximab-based primary chemoradiation in an academic setting at Loma Linda University Medical Center. We also re-analyzed the HNSC dataset from The Cancer Genome Atlas (TCGA) [11] to clarify the relationship between HPV and EGFR statuses in HNSCC.

Data collection
ICD-9, ICD-10, and CPT codes were used to search the Loma Linda University Health Cancer Registry to find patients diagnosed with HNSCC between 2006 and 2018. This study was approved by Loma Linda University Medical Center Institutional Review Board (IRB Approval #: 5180298). The following data were obtained for each patient: age, sex, smoking status, primary malignancy site, pathology report, staging, type of radiation and number of radiation treatments, chemotherapy regimen, and number of chemotherapy cycles completed. Radiation dose ranged between 48 and 72 Gy.

Patient selection
Eligible patients were between the ages of 18-99 years who had locally advanced head and neck cancer with initial stages III-IVB receiving concurrent chemoradiation with either cisplatin or cetuximab as first-line therapy. Primary tumors of the oral cavity, oropharynx, and hypopharynx/larynx were included. We excluded those who underwent surgery as first-line therapy, concurrent chemoradiation as second-line or salvage therapy for recurrent or metastatic disease, underlying malignancy other than head and neck cancer, those who did not receive either cisplatin or cetuximab as part of chemotherapy regimen, and nasopharyngeal tumors.
Cases that met inclusion criteria were then separated by chemotherapy received. Categorical variables analyzed included smoking and HPV/p16 statuses, which was abstracted from pathology reports consistent with College of American Pathologists recommendation [12]. p16 INK4a immunohistochemistry stain and HPV in situ hybridization were performed in Clinical Laboratory Improvement Amendments regulated laboratories with in vitro diagnostic antibodies. Patients with a smoking history were further categorized into light smoking (< 10 pack-years) and heavy smoking (≥ 10 pack-years). Comorbidities was considered positive if patients had ≥ 2 comorbidities and negative if < 2.

Endpoints and statistics
Primary endpoint was overall survival (OS) by treatment with either cisplatin or cetuximab. OS was analyzed by the Kaplan-Meier and log-rank methods. Survival was compared by univariate Cox proportional hazards model between treatment groups. Survival analyses were stratified by HPV/p16 and smoking statuses. Statistical analysis with p-values of < 0.05 was considered significant. Statistics were performed with R packages "survival" and "survminer" (Vienna, Austria).

TCGA data and analysis
Publicly available data for clinical and phenotypic information, gene expression (by RNA sequencing), and copy number (generated by the Affymetrix Genome-Wide Human SNP Array 6.0 platform) data of the HNSC cohort from TCGA were obtained from University of California Santa Cruz Xena Browser. Gene expression data were represented as RSEM scores, which were log2transformed normalized counts [13]. The copy number estimated values are thresholded to −2, −1, 0, 1, 2, representing homozygous deletion, single copy deletion, diploid normal copy, low-level copy number amplification, or high-level copy number amplification reported by GISTIC2 [14,15]. EGFR copy number statuses were grouped to amplified (GISTIC2 score ≥ 1) and nonamplified (GISTIC2 score ≤ 0). HPV status was obtained from the supplementary information of the original Nature article [11], and most of them were ascertained by the presence of HPV transcripts or genomes by whole genome/exome and RNA sequencing. All analyses were performed on KNIME Analytics.

Patient and tumor characteristics
A total of 1545 patients were retrieved from the LLUMC Cancer Registry between 2006 and 2018. Of these patients, 121 met inclusion criteria and were further divided into cisplatin (n = 66) and cetuximab (n = 55) cohorts (Fig. 1). A summary of demographic information can be found in Table 1.

Improved OS in HPV/p16-positive cancer treated with cisplatin-based chemoradiation
Among the patients who were HPV/p16-positive (n = 55), those who received cisplatin chemoradiation had longer OS. The median OS for patients with HPV/ p16-positive cancer treated with cisplatin-based therapy was not reached compared to 60 months for HPV/ p16-positive cancer treated with cetuximab (p = 0.036, HR = 0.25 [95% CI 0.061-1.00]) (Fig. 2b).

Cisplatin chemoradiation improved OS in patients with positive smoking history
In patients with a smoking history (n = 76), cisplatinbased radiotherapy was associated with longer OS. The median OS in the cisplatin group was not reached, while that in the cetuximab cohort was 60 months (p = 0.03, HR = 0.36 [95% CI 0.14−0.93]) (Fig. 2c).

TCGA HNSC data re-analysis
Within TCGA who had HPV-positive cancers, none of the oropharyngeal (n = 22) and only one of the overall head and neck patients (n = 36) had the amplified EGFR gene region, whereas within the HPV-negative cohort, six oropharyngeal (n = 11, 54.5%) and 124 of the overall head and neck patients (n = 243, 51.0%) had the amplified EGFR gene region. Fisher's exact tests indicated that the HPV-negative cohort is more likely to possess EGFR amplification in head and neck patients (p < 0.0001). At the transcription level, RNA expressions of the EGFR   gene in HPV-negative cancers were 1.619 times (95% CI 1.22 to 2.14) higher than HPV-positive cancers in the overall head and neck cohort (p < 0.0001) (Fig. 3).

Discussion
In this single institution retrospective study, we investigated real-world outcomes of locoregionally advanced HNSCC treated with primary chemoradiation with cisplatin versus cetuximab. Our finding of an OS benefit in HPV/p16-positive cases treated with cisplatin-based therapy compared to cetuximab is consistent with recent phase 3 clinical trial data [8,9] and national database studies [16][17][18]. While our study and the VA study by Bauml et al. both found that cetuximab with radiation yields inferior OS, more than 99% of the VA study population are male and it did not perform a subgroup analysis of HPV status. This growing evidence supports cisplatin-based radiotherapy as the standard of care for patients with HPV/p16-positive cancer with low risk (e.g. non-smokers or < 10 pack-years smoking history) [9]. We also found the survival benefit with cisplatin therapy to be consistent among those who smoke and those with advanced age. However, cetuximab likely still will play a role in patients with poor renal function, as both even though head to head trials suggested no different overall toxicity, cisplatin consistently demonstrated increased rates of acute kidney injury [8,9].
Some authors have proposed that the inferior survival outcomes in patients with HPV associated oropharyngeal HNSCC who received concurrent chemoradiation with cetuximab instead of cisplatin might be related to differences in EGFR expression and HPV status. Indeed, we observed that amplification of the EGFR gene region was rare to absent in HPV-positive cancers, while about half of the HPV-negative cases possessed different degrees of amplifications in the TCGA HNSC dataset. Expression of the EGFR gene was also significantly lower in HPV-positive HNSCC, consistent with prior reports [19]. However, EGFR expression has not been shown to be predictive of clinical benefit for anti EGFR therapy in SCCHN, which may be related to the lack of correlation between EGFR expression and autophosphorylation activity [20,21].
The main limitation of this study is that, as a retrospective study, we cannot exclude possible confounding factors that may contribute to inferior OS of cetuximabbased radiotherapy in patients with HPV/p16-positive cancers, such as insufficient renal function that have precluded a cisplatin regimen or the selection bias of cetuximab in elderly and frail patients. However, based on our data even the population with advanced age still benefited from high dose cisplatin, and further more patients with at least 2 comorbidities received cisplatin treatment. In conclusion, our result was consistent with the recent prospective randomized clinical trials, which have provided strong evidence of the superiority of cisplatin compared with cetuximab in HPV/p16-positive cancers [8,9].
Abbreviations HNSCC: Head and neck squamous cell carcinoma; TCGA : The Cancer Genome Atlas; OS: Overall survival; EGFR: Epidermal growth factor receptor; HPV: Human papillomavirus.