SEATTLE (AP) — Billionaire Seattle Seahawks owner and Microsoft co-founder Paul Allen says cancer he was treated for in 2009 has returned.

Allen said on Twitter Monday that he recently learned of the non-Hodgkin’s lymphoma and plans to fight it aggressively.

He says there have been advances in medicine since he overcame the disease nearly a decade ago and that he and his doctors are optimistic that he will see good results from the latest therapies.

The 65-year-old says he will continue to stay involved with his Vulcan real estate company, the Allen Institutes, the Seahawks and Portland Trail Blazers and has confidence in leadership teams to manage operations while he undergoes treatment.

He also expressed gratitude for support from family and friends and that he appreciated everyone’s support in the past.