Jenna Fischer Shares How Cancer Changed Her Outlook on Life

Jenna Fischer is feeling grateful to be alive ... revealing how her breast cancer battle has taught her to ignore the everyday annoyances that come with living in a big city.

"The Office" actress stopped by the "Today" show Monday, where she sat down with Hoda Kotb to discuss her fight with breast cancer ... and how it's left a lasting impact on her.

Jenna, who earlier this month shared she had been diagnosed with a rare and aggressive form of breast cancer, said "the most important things became so clear so quickly" after receiving her jarring health news.

She explained ... "I find the world to be such a beautiful place in all of its quirkiness. Even things that used to irritate me, I now sometimes find charming."

For instance, traffic, which is notoriously bad in the City of Angels, is merely "cute" to her now.

Of course, her optimistic outlook wasn't there from the start ... with Jenna admitting she was initially irritated by her medical tests, calling her routine mammogram "annoying."

Jenna's now so grateful she kept her annual appointment ... describing how she learned about her cancer diagnosis while checking her medical portal during a hike.

She continued ... "That's when I saw words like, 'invasive,' 'ductal,' 'carcinoma,' 'malignant.' I was like, 'Those words sound like cancer words.'"

From there, Jenna underwent a lumpectomy in January and 12 rounds of chemo, and 3 weeks of radiation. Jenna admitted she was worried about losing her hair at first ... noting she used to comb over her locks to cover her bald spot during treatment.