The Mount Nittany Medical Center says Paterno died because of metastatic small cell carcinoma of the lung.
That is a way of saying Paterno's lung cancer had spread.
Eyewitness News sat down with Dr. Brian Mott, a cardio-thourasic surgeon, at Scranton's Community Medical Center Monday.
He deals with cases of lung cancer on a daily basis and explained the lung cancer.
"Joe Paterno's lung cancer was a type of lung cancer called small cell lung cancer. There are two types. Non-small cell and small cell," Dr. Mott said. "Not only did he have small cell which is a very aggressive form of cancer, he also had metastatic small cell lung cancer."
Doctor Mott says only 15-percent of lung cancer cases are small cell cases.
With Paterno being 85-years-old, Mott says doctors could only treat Paterno with chemotherapy and possibly radiation.
"With the diagnosis he had, his chances of surviving any further than six months was probably, almost zero," Dr. Mott said. "The treatment that he got, although they said treatable in the newspaper, he was being treated but it definitely was not curable."
Back in November, it was Paterno's son who classified the lung cancer as treatable.
"There was nothing they could do for him surgically," Dr. Mott said. "They were treating him in order to prevent his symptoms from getting any worse."
Doctor Mott says he thinks Paterno's death will bring more attention to lung cancer cases.
He showed us statistics from 2008 on cancer deaths from men and women.
Lung cancer killed 31-percent of all the men who died of cancer.
"It's the most lethal type of cancer we have and we know about and it's one of the most common types and incidents continue to rise," Dr. Mott said.