The legendary disco and soul singer passed away from the disease yesterday (May 17) at the age of 63.
Summer lived in an apartment near Ground Zero in New York City on the day of the tragedy in 2001, and allegedly believed that inhaling toxic dust particles led to her illness.
In the months and years after 9/11, Summer would constantly spray disinfectant in the air, a source told TMZ.
Dance Fever host Deney Terrio also revealed that Summer would often hang silk sheets in her dressing room in order to stop dust coming inside.
Another insider claims that Summer felt that the 9/11 events were an attack on Christianity, and that she was a target because of her religious beliefs.
At least 55 rescue workers have died due to cancer since 9/11, although several had already been diagnosed before the attacks. Since 9/11, 75 have been diagnosed with cancer, with over 18,000 people claiming that they have fallen ill due to inhaling toxic dust particles.
Kylie Minogue, Nicki Minaj and Ryan Seacrest were among a host of celebrities who have spoken out in tribute to the late singer.
Photo gallery - Donna Summer's life in pictures:
Copyright: Rex Features Andre Csillag/Rex Features
Watch the video for Donna Summer's 'State of Independence' below: