Source: ww.pharmacytimes.com
Author: Bryan Fitzgerald, PharmD, BCOP
Health-System Edition, July 2021, Volume 10, Issue 4

Oropharyngeal cancer (OPC) is a type of head and neck cancer that affects structures in the back of the throat, including the base of the tongue, the posterior pharynx, the soft palate, and the tonsils.1 In the United States, rates of OPC are increasing each year, with an estimated 54,010 new cases in 2021.2 Well-established risk factors include alcohol abuse; exposure to tobacco, including chewing tobacco, cigarettes, and pipes; and infection with human papillomavirus (HPV).

With an estimated 43 million infections in 2018, HPV is the most common sexually transmitted infection in the United States.3 HPV infection is causally linked with cancers of the anogenital region, including anal, cervical, penile, vaginal, and vulvar cancers. When HPV is spread orally, infections can also lead to the development of OPC. In the United States, more than 70% of OPC cases are caused by HPV.4

HPV is a group of more than 100 viruses, including certain high-risk strains associated with the development of cancer. The HPV-16 strain is responsible for causing the majority of HPV-positive (HPV+) OPC cases, with HPV-18, HPV-33, and HPV-35 also contributing, albeit significantly less than HPV-16.1 In these high-risk HPV strains, the viral genome encodes several oncogenic proteins that inhibit tumor suppressor proteins, leading to chromosomal instability and malignancy in infected cells.

HPV+ OPC is considered a genetically distinct form of OPC. Compared with HPV-negative (HPC–) OPC cases, HPV+ OPC is associated with a favorable prognosis with improved rates of response prognosis with improved rates of response to treatment and overall survival. Because of the difference in tumor biology, the National Comprehensive Cancer Network (NCCN) has adopted different staging criteria for HPV+ and HPV– disease and recommends that HPV status be used to stratify patients with OPC.1

The treatment landscape for localized OPC typically involves a multidisciplinary approach consisting of chemotherapy, radiation, and/or surgery. For fit patients with locally advanced OPC who are able to tolerate intensive therapy, concurrent radiation with systemic high-dose cisplatin chemotherapy is the preferred treatment regimen.1 Unfortunately, treatment of OPC is associated with a high risk of treatment-related morbidity, which may leave patients cured of their malignancy but with lifelong complications, such as dysgeusia, dysphagia, and xerostomia, but also systemic complications from cisplatin chemotherapy, including hearing loss and neurotoxicity.

Because patients with HPV+ OPC are generally younger with more favorable prognoses, clinicians have hypothesized that less intensive treatment could result in fewer long-term complications from treatment but with continued favorable cancer-related outcomes.5 This concept, called deintensification, has become popular in recent years. Several strategies for treatment deintensification have been proposed, including reducing the dose of radiation; substituting cisplatin for an alternative agent with less toxicity, such as cetuximab; and surgical resection. Several phase 3 comparison trials have been conducted, and other trials are ongoing.

Aptly named De-ESCALaTE (NCT01874171), this phase 3 trial randomized patients with 334 HPV+ OPC to receive radiation plus cetuximab or cisplatin.6

Unfortunately, the trial results did not favor substitution of cisplatin with cetuximab. At 2 years, the incidence of severe toxicities did not significantly differ between cetuximab and cisplatin (P = .98), nor did rates of overall toxicities (P = .49). Significant differences in 2-year overall survival rates and recurrence rates were seen. However, these results favored cisplatin (HR, 5.0; P = .001 for overall survival; HR, 3.4; P = .0007 for recurrence).6

RTOG-1016 (NCT01302834) was a second phase 3 trial published comparing cetuximab with cisplatin in HPV+ OPC patients.7 This trial analyzed 805 patients who were randomized to receive radiation plus cetuximab or cisplatin. Similar to the De-ESCALaTE trial, the RTOG-1016 trial results favored cisplatin over cetuximab, with 5-year overall survival rates of 84.6% versus 77.9%.8

Because of the De-ESCALaTE and RTOG-1016 results, experts advise against the substitution of cisplatin for chemoradiation regimens for patients with localized HPV+ OPC, and cisplatin plus radiation continues to be the preferred systemic treatment option per the NCCN guidelines.1,5 Because cisplatin continues to be standard of care for the treatment of localized OPC, the role of deintensification for patients with HPV+ OPC may lie in adjustments to surgical strategies or radiation therapy. Treatment deintensification should be pursued only through clinical trials, and experts encourage clinicians to conduct and analyze phase 2 trials before moving on to phase 3 studies.1,5

CONCLUSION
The treatment landscape of cancer is ever-changing. Specifically in localized HPV+ OPC, the difference in tumor biology presents a unique clinical area where reducing the intensity of treatment may be warranted, particularly with long- and short-term toxicities associated with cisplatin. Interestingly, phase 3 data have shown evidence of harm in removing cisplatin from chemoradiation regimens for HPV+ OPC; therefore, cisplatin-based chemoradiation remains the standard of care for these patients. Future trials may support treatment deintensification in ways other than removing cisplatin.

REFERENCES
1. NCCN. Clinical Practice Guidelines in Oncology. Head and neck cancers, version 3.2021. Accessed June 16, 2021. https://www.nccn.org/professionals/physician_gls/pdf/head-and-neck.pdf

2. Cancer stat facts: oral cavity and pharynx cancer. National Cancer Institute. Accessed June 16, 2021. https://seer.cancer.gov/statfacts/html/oralcav.html

3. Genital HPV infection – fact sheet. CDC. Updated January 19, 2021. Accessed June 17, 2021. https://www.cdc.gov/std/hpv/stdfact-hpv.htm
4. HPV and oropharyngeal cancer. CDC. Updated September 3, 2020. Accessed June 17, 2021. https://www.cdc.gov/cancer/hpv/basic_info/hpv_oropharyngeal.htm

5. Mehanna H, Rischin D, Wong SJ, et al. De-escalation after DE-ESCALATE and RTOG 1016: a head and neck cancer intergroup framework for future de-escalation studies. J Clin Oncol. 2020;38(22):2552-2557. doi:10.1200/JCO.20.00056

6. Mehanna H, Robinson M, Hartley A, et al; De-ESCALaTE HPV Trial Group. Radiotherapy plus cisplatin or cetuximab in low-risk human papillomavirus-positive oropharyngeal cancer (De-ESCALaTE HPV): an open-label randomised controlled phase 3 trial. Lancet. 2019;393(10166):51-60. doi:10.1016/S0140-6736(18)32752-1

7. Gillison ML, Trotti AM, Harris J, et al. Radiotherapy plus cetuximab or cisplatin in human papillomavirus-positive oropharyngeal cancer (NRG Oncology RTOG 1016): a randomised, multicentre, non-inferiority trial. Lancet. 2019;393(10166):40-50. doi:10.1016/S0140-6736(18)32779-X

8. Gardasil 9. Prescribing information. Pfizer; 2017. Accessed June 23, 2021. https://www.fda.gov/fi les/vaccines,%20blood%20&%20biologics/published/Package-Insert—Gardasil.pdf

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