Amanda Dempsey, who was diagnosed with ovarian cancer in 1997, was surrounded by family at the time of her death.
She worked as a secretary in the Buckfield Junior/Senior High School for years before retiring in 2013.
In 2008, The Grey's Anatomy actor and his sisters founded The Patrick Dempsey Center for Cancer Hope & Healing with the Central Maine Medical Center in Lewiston, Me., where their mother was treated.
The center provides free cancer education, support and integrated medicine to those affected by cancer.
"Mom was a humble, beautiful spirit, with great courage who lived life in the present and gave hope to all," Mary Dempsey, Patrick Dempsey's sister, said in a statement.
The president and CEO of Central Maine Healthcare also addressed Amanda Dempsey's death, saying she had been "both a great lady and a determined fighter who displayed tremendous courage, class and grace during her long battle with cancer."