Willis, a breast cancer survivor, admitted she debated opening up about her "embarrassing" diagnosis and urged the public to get vaccinated.
The mum-of-two underwent several rounds of chemotherapy before having both breasts removed in a bid to prevent the disease spreading.
There was little to no increase in breast cancer risk for semi-permanent or temporary dye use.
Secondary Sisters aims to change perceptions of people living with incurable cancer and support those in the same position.
The singer's 67-year-old father is set to reveal his breast cancer battle on 'Good Morning America'.