Exhibit 99.1

JOINT FILING AGREEMENT

The undersigned hereby agree that Amendment No. 3 to the Schedule 13G, dated as of February 12, 2018, with respect to the Common Stock of Karyopharm Therapeutics Inc. is, and any amendments thereto, any Schedule 13D with respect to such Common Stock, and any amendments thereto, signed by each of the undersigned shall be, filed on behalf of each of us pursuant to and in accordance with the provisions of Rule 13d-1(f) under the Securities Exchange Act of 1934.

Dated: February 12, 2018   Chione Ltd., by /s/ Simon Prisk, as attorney-in-fact   Marcin Czernik, by /s/ Simon Prisk, as attorney-in-fact   Andreas Hadjimichael, by /s/ Simon Prisk, as attorney-in-fact   George Hadjimichael, by /s/ Simon Prisk, as attorney-in- fact   Wiaczeslaw Smolokowski, by /s/ Simon Prisk, as attorney-in-fact