All TCS New York City Marathon fees are non-refundable. If you cancel your entry, it cannot be reinstated for the current year's TCS New York City Marathon. If you cancel this year (and did not cancel last year) and you want to guarantee your entry for the following year, you'll need to apply for the upcoming race during the application window and pay the processing and entry fees required.
Runners who have guaranteed entry to the 2018 race because they canceled in 2017 cannot cancel a second time and become eligible for guaranteed entry in 2019. More information can be found on the TCS New York City Marathon website.