Background and objective: We have already demonstrated that post-operative concentration of salivary interleukin-6 (IL-6) may predict early locoregional recurrence in oral squamous cell carcinoma (OSCC) (Head & Neck; 2012). This previous report demonstrated that 11 (41%)of the 27 patients developed locoregional recurrence within 24 months after surgery, and post-operative salivary IL-6 concentration was an independent risk factor for locoregional recurrence at this time. We kept monitoring salivary IL-6 concentration, and sought to elucidate the correlations between salivary IL-6 concentration and late locoregional recurrence in OSCC.

Methods: We included 27 consecutive patients with OSCC who underwent radical surgery in this study with written informed consent. Stimulated saliva was collected three times (before and twice in after surgery). The average time of the collection of post-operative saliva was 1.0–0.6 month (PO1) and 33.4–4.5 months (PO2), respectively. We compared the concentration of salivary IL-6 in PO2 and locoregional recurrence after 24 months of the treatment.

Results: Of the 27 patients, 3 patients died and 2 patients dropped from the regular follow-up within 24 months after surgery. Of the 22 patients, 4 patients were diagnosed with locoregional recurrence after 24 months of the surgery. The median concentrations of IL-6 at the time of PO1 and PO2 were 2.1 (range 0.3–126) pg/mL and 0.5 (0.3–38.7) pg/mL, respectively ( P = 0.006). The median post-operative concentration of IL-6 in PO2 was significantly higher in patients with than without locoregional recurrence (median; 5.2 pg/mL vs. 0.4 pg/mL: P = 0.03).

Conclusions: Continued monitoring of salivary interleukin-6 levels may be useful for predicting not only early but also late locoregional recurrence in patients with OSCC.