The lifelong Democratic activist is 77 years old and took office in January 2003 along with Gov. Ed Rendell.
Knoll is a native of the Pittsburgh suburb of McKees Rocks.
She explains her illness in an open letter on her official Web site. Knoll says in the letter that she was diagnosed earlier this summer with neuroendocrine illness, aformer of cancer.
Knoll says she's responding well to treatments and feels fine.
On the Net: http://www.ltgovernor.state.pa.us