The Contribution of Intensity-Modulated Radiotherapy after Non-curative Intent Surgery for Head and Neck Adenoid Cystic Carcinoma

Abstract

Incomplete surgery (gross total resection, near total resection, and subtotal resection) of head and neck adenoid cystic carcinoma (HNACC) is controversially considered as an unfavorable prognostic factor as to curative intent surgery (CIS). However, in Intensity-Modulated Radiotherapy (RT) era, after planed incomplete surgery (PIS), intensified RT or RT with concurrent chemotherapy (CCT) may contribute to tumor control and survival. Thus, we investigated the contribution of IMRT after PIS on local control and survival in HNACC. Retrospective review was performed for 170 consecutive patients with HNACC treated with curative postoperative IMRT with or without concurrent chemotherapy, between 2015 and 2018, after PIS (n = 102) or CIS (n = 68). All plan target volumes were designed to including the primary tumor and related cranial nerve pathway. Patients with other malignant tumors or distant metastasis were excluded. Among the 170 patients (98 women and 72 men; median age, 53 years), the median follow-up time was 27.8 (range, 9.6-59.1) months. The estimated 3-year local-regional recurrence-free survival (LRRFS) rate, progression-free survival (PFS) rate, overall survival (OS) rate, and distant metastasis-free survival (DMFS) rate were 92.4% (95%CI: 87.3-95.9), 74.7% (95%CI: 67.5-81.0), 98.5% (95%CI: 94.9-99.6), and 76.0% (95%CI: 68.7-82.1), respectively. Patients with high grade, Ki-67≥10%, Stage III-IV, extra-nodal extension (ENE), perineural invasion (PNI) and positive margin was associated with worse PFS (p<0.0001, p = 0.002, p = 0.003, and p = 0.0004, p = 0.042, and p = 0.021, respectively). The baseline and treatment characteristics were equally distributed between PIS and CIS group, except that there were more patients with positive margin and received RT dose≥66 Gy in PIS group (p = 0.000 and p = 0.000). There was no difference in LRRFS, DFS, OS, and DMFS between two groups, both in stage I-II and Stage III-IV (p = 0.280, p = 0.371, p = 0.752, and p = 0.549, respectively). Among patients with high grade, Ki-67≥10%, ENE or PNI, there was also no difference in PFS between two groups. Among patients received radiation dose<66Gy, PIS group patients had significant worse PFS (p = 0.029), while among patients without any CCT, PIS group patients had marginal significant worse PFS (p = 0.067). In IMRT era, PIS does not compromise oncologic treatment, even in patients with worse prognostic factors; however, Doses of ≥66 Gy or CCT might be essential. This strategy warrants further evaluation in prospective randomized trials with longer follow-up.