How to cache callback result

[boochamoocha]

Hi all. Need advise.
I'm trying to cache like this, but nothing happens.

const express = require('express');
const router = express.Router();
const apicache = require('apicache');
const backend = require('../integrations/backend');
let cache = apicache.middleware;

router.get('/events', cache('5 minutes'), function(req, res, next) {
    backend.getEvents('',(result, error) => {
        if (error) {
            return;
        }
        res.setHeader('Content-Type', 'application/json');
        res.send(result);
    });
});

But if a get info from backend in sync manner - cache works.