A Phase I Study of the CDK4/6 Inhibitor Palbociclib in Combination with Cetuximab and Radiotherapy for Locally Advanced Head and Neck Squamous Cell Carcinoma.

PURPOSE: Palbociclib, a cyclin D kinase 4 (CDK4)/6 inhibitor, has shown radiosensitizing effects in preclinical studies. There is a strong rationale for adding palbociclib to cetuximab and radiotherapy in locally advanced head and neck squamous cell carcinoma (LA-HNSCC), especially in p16-negative HNSCC. PATIENTS AND METHODS: We conducted a phase I dose-escalation study (NCT03024489) using a classical 3+3 design to determine safety, tolerability, and MTD of palbociclib, cetuximab, and intensity-modulated radiotherapy (IMRT) combination. At the recommended phase II dose (RP2D), additional p16-negative patients were enrolled. RESULTS: Twenty-seven patients with LA-HNSCC (13 in dose escalation, 14 in expansion) with oropharyngeal (41%) and hypopharyngeal (30%) cancers were enrolled. The MTD was not reached, and the RP2D of palbociclib was established at the full standard palbociclib dose of 125 mg/day for 21 days per cycle, administered for two cycles during IMRT. The most common grade 3-4 toxicities were mucositis (59%), radiation dermatitis (22%), and neutropenia (22%), with a febrile neutropenia rate of 7%. Common genomic alterations included mutations in TP53 (57%), GNAQ (35%), and PIK3CA (17%), and copy-number gains in CCND1 (22%), CCND2 (9%), and EGFR (9%). Overall, p16 expression was positive in 15% of patients. No correlation was observed between p16 status, genomic alterations, and preliminary efficacy. The objective response rate was 84%. The rates for 2-year locoregional control, event-free survival, and overall survival were 73%, 48%, and 71%, respectively. CONCLUSIONS: The palbociclib, cetuximab, and IMRT combination was well tolerated. The RP2D was established, while no MTD was determined. The regimen demonstrated promising preliminary efficacy, suggesting further investigation is warranted in patients with cisplatin-ineligible p16/human papilloma virus-unrelated LA-HNSCC.

Characteristics and Impact of HPV-Associated p16 Expression on Head and Neck Squamous Cell Carcinoma in Thai Patients.

BACKGROUND: Head and neck squamous cell carcinoma (HNSCC) is a common malignancy in Asia. Infection by human papilloma virus (HPV) has been recognized as an etiological risk for HNSCC, especially oropharyngeal region. While the association between HPV and HNSCC has been well evaluated in Western countries, only a few investigated the HPV-associated HNSCC in Southeast Asia. This study evaluated the prevalence, the characteristics, and the impact of HPV on the treatment outcomes in Thai HNSCC patients. METHODS: Non-nasopharyngeal HNSCC patients treated at Ramathibodi Hospital during 2007-2013 were identified through the cancer registry database. Baseline patient, treatment data and survivals were retrospectively reviewed. The formalin-fixed paraffin-embedded (FFPE) tissue sections were retrieved for p16 analysis. The HPV status was determined by p16 immunohistochemistry. The survival outcomes were analyzed in cases which p16 status was confirmed. RESULTS: Total of 200 FFPE tissues of HNSCC patients was evaluated for p16 expression. Positive p16 status was observed in 24 cases (12%); majority of p16-positive were men (20:4 cases). The oropharynx (37.9%) was the most common site found in p16-positive while oral cavity (3.2%) was the least common site. Interestingly, 66.7% of p16-positive were former/current smokers, and 70.8% of this subgroup was categorized as clinical AJCC stage III-IV. The p16-positive HNSCC was significantly superior in 5-year overall survival [5-yrs OS 63% vs. 40%, p=0.03], 5-year disease-free survival [5-yrs DFS 61% vs. 36%, p=0.03] and in 5-year locoregional relapse-free survival [5-yrs LRFS 93% vs. 68%, p=0.018] when compared with p16-negative. CONCLUSIONS: In comparison to the results from the Western countries, the prevalence of HPV-related HNSCC in Thai patients was less, and differences in some characteristics were observed. Nevertheless, improvement in OS, DFS and LRFS were observed in p16-positive patients. Our analyses suggested that p16 status is also a strong prognostic marker for HNSCC patients in Thailand.