Adjuvant proton beam irradiation for invasive conjunctival squamous cell carcinoma: systemic, ocular and visual outcomes.

AIMS: Invasive conjunctival squamous cell carcinoma (cSCC) carries a risk of local/distant recurrence after surgical excision. Adjuvant treatment is therefore required. We aimed to evaluate the outcome of adjuvant proton beam therapy (PBT) after excision of cSCC, in terms of overall survival, local/distant recurrence, eye conservation and vision. METHODS: Consecutive patients with invasive cSCC, who received PBT (60 Gy in 8 fractions based on preoperative photographs/drawings without tantalum clips) within 4 months of excision between 2006 and 2019, were retrospectively included. Cases with xeroderma pigmentosum were excluded. Follow-up included neck ultrasound or positron emission tomography-scan every 6 months for at least 2 years. RESULTS: 66 patients were included (50 men, 16 women, mean age 67.4±13.4 years). Two presented immunosuppression. Over a mean follow-up of 3.7 years, tumour control was achieved in 63 patients (95.5%). Three patients presented local recurrence (4.5%), including two in situ cSCC and one dysplasia with a mean delay of 12.6-month after PBT. Relapsing patients had larger lesions (p=0.041) and more frequent fornix/tarsal conjunctiva involvement (p=0.010) at diagnosis. No patient developed metastases from cSCC. Four patients died during follow-up (6.0%): two from other cancers and two from unknown causes. One patient developed neovascular glaucoma requiring secondary enucleation. 42 patients (64%) retained visual acuity better than 20/30 at the last visit. CONCLUSION: Adjuvant PBT for invasive cSCC provides excellent local control and is associated with favourable systemic, ocular and visual outcomes. PBT with tantalum clips, or alternative irradiation modalities, should be considered for large tumours extending to the tarsal conjunctiva.