The death this week of the iconic 9/11 "dust lady" has again shed light on the thousands of cancer cases some believe are linked to the 2001 terrorist attack.

Marcy Borders, who was photographed covered in ash as she escaped the World Trade Center's North Tower on Sept. 11, 2001, died this week of stomach cancer at age 42. She suspected that the carcinogen-laced dust that filled the air 14 years ago caused her illness.

"I'm saying to myself 'Did this thing ignite cancer cells in me?'" Borders told the Jersey Journal after her diagnosis in 2014. "I definitely believe it because I haven't had any illnesses. I don't have high blood pressure….high cholesterol, diabetes."

"How do you go from being healthy to waking up the next day with cancer?" she asked the newspaper's reporter.

Borders was working at Bank of America on the 81st floor of the World Trade Center's north tower on the day al Qaeda members flew two hijacked planes into the building. Borders survived the attack but developed severe depression as a result of the trauma and later became addicted to alcohol and drugs. In 2014, she was diagnosed with stomach cancer.

"How do you go from being healthy to waking up the next day with cancer?"

Borders was one of the thousands of people at the World Trade Center site who suffered health problems in the aftermath of the attack, including respiratory issues and psychological trauma. But Borders never conclusively proved that her cancer was caused by the attack, pointing toward the controversial legacy that still remains from 9/11, as more people who were at ground zero are being diagnosed with cancer more than a decade later.

Scientists have remained divided as to whether the toxins in the dust of the 9/11 attack caused cancer, with many arguing that there is not enough evidence to link cancer to exposure at Ground Zero. A 2012 study examined more than 55,000 New Yorkers who were at ground zero and found no significant associations between exposure and an increased likelihood of cancer. The researchers did, however, find slightly increased rates of prostate cancer, thyroid cancer, and myeloma, but recommended further study in order to conclusively prove a decisive link.

It was not until 2012, after the passage of the James Zadroga 9/11 Health and Compensation Act that the government agreed to pay for the cancer treatment of those who were exposed to ground zero site under the federally funded World Trade Center Health Program. The decision to include cancer in the WTC program only came after a 2011 study showing that firefighters who worked at ground zero were almost 20 percent more likely to develop cancer than firefighters who did not.

Beforehand, the government only paid for health problems that were demonstrably caused by 9/11, such as respiratory issues and mental trauma, of which there has been extensive research showing links to 9/11.

In the immediate aftermath of 9/11, there was intense criticism toward New York Mayor Rudy Giuliani and Environmental Protection Agency Administrator Christine Todd Whitman, including multiple class action lawsuits arguing that the city did not do enough to prevent people from exposure to toxic dust that could potentially cause dangerous diseases. Giuliani and Whitman repeatedly said that the air was safe to breath and moved quickly to reopen Lower Manhattan days after the attack, despite the yet-unknown effects the toxins at the site would have on people.

"The mix of toxins down there was simply indescribable," Michael Crane, Director of the World Trade Center Health Program at Mount Sinai, which treats and monitors 9/11 first responders and victims, told VICE News. "No one will ever know what was in that dust cloud that hit this lady."

Crane is certain that there is a link between cancer and exposure to the toxins at the World Trade Center site. But since cancer, unlike asthma or PTSD, takes years to develop, it is more difficult for doctors to prove a direct link to 9/11 exposure, especially since it is unclear exactly what chemicals people were exposed to in the first place.

Crane says there were at least 90,000 first responders at 9/11 and his program has monitored or treated two-thirds of them. But, Crane says he is certain there are many more people who were exposed to ground zero who likely are suffering from the long term effects of the dust cloud, or who will at some point in their lifetimes, but have not sought out treatment from the WTC program.

For instance, scientists knew there was asbestos, a known carcinogen, in the cloud since it had been used in the construction of the Twin Towers in the late 1960s. But it can be 20 years before someone exposed to asbestos begins showing adverse health consequences caused by it, says Crane, and by then, many people do not think to connect the cause of their disease to 9/11.

Borders could have theoretically gotten the government to fund her expensive cancer treatments if she proved it was caused by 9/11. Last year, she told the Jersey Journal that she had racked up almost $200,000 on medical fees and could no longer afford to buy her medication.

Borders' case is not unique. Last September, three New York City firefighters who were at ground zero all died from cancer on the same day.

"I've been to 54 funerals of firefighters since 9/11 and 52 of them are cancer-related," John Feal, a former firefighter and founder of an advocacy organization for 9/11 first responders, told ABC News in 2011.