Characteristics of Very Long Responder to Maintenance Cetuximab after a Platinum-Cetuximab Based Chemotherapy for Recurrent And/or Metastatic Head and Neck Squamous Cell Carcinomas (RM HNSCC).

e17524 Background: Standard treatment for first line RM HNSCC is the association of platinum-5FU and cetuximab. For non-progressive patients (pts), cetuximab is given weekly as maintenance until progression or unacceptable toxicity. In the EXTREME protocol (Vermorken et al, NEJM 2008), this strategy showed an OS of 10.1 months with a mean duration of maintenance of 3 months. This study aimed at describing pts who have benefited from a cetuximab maintenance for a longer period (i.e. > 6 months). Methods: We did a retrospective study in 7 centers in France. Inclusion criteria were: pts > 18 years with a RM HNSCC treated between November 2009 and January 2017, with platinum based chemotherapy and cetuximab followed by weekly cetuximab maintenance of more than 6 months. Results: 53 pts (45 male), with a median age of 57 [38-76] were recorded. Median follow-up was 63.7 months [14.8-237.6]. 72% [37/53] had an oral cavity or oropharynx tumor location with a well or moderately differentiated carcinoma (74%). 45/53 (85%) were smokers and 4/21 (19%) p16 positive. 46/53 (87%) had a Performans Status of 0-1. Mean BMI and albumin level were respectively 22.5 [SD: 4.19] and 40g/l [SD: 4.9]. EXTREME regimen was used for 44 pts, 2 pts had platinum and cetuximab and 7 received platinum, docetaxel and cetuximab. Mean number of chemotherapy cycles was 5 [3-7]. After chemotherapy, the number of pts with complete response (CR), partial response (PR) or stabilization was respectively 5 (9%), 23 (43%) and 25 (47%). 2 pts in PR finally achieved CR during maintenance. One of them stopped cetuximab and was still in CR 5 months later. Mean duration time of maintenance by cetuximab was 11 months [6-24]. Toxicities were mainly cutaneous: 47/53 pts had toxicities, of which 6 had grade 3. Presence of cutaneous toxicities seemed to be correlated with a longer response (p = 0.01). PFS and OS were respectively 15.5 and 27.4 months. Conclusions: Our study allowed us to identify a cohort of long responder pts to maintenance cetuximab including 2 pts who obtained a complete response. More analysis should be done to identify biomarkers able to predict long responder.