Angela Kinsey's promise to The Office co-star Jenna Fischer after breast cancer diagnosis

The Office star Angela Kinsey has shared a sweet tribute to her former co-star, best friend and podcast co-host Jenna Fischer after she revealed she was recently diagnosed with an "aggressive" form of breast cancer.

Fischer, 50, this week shared a moving post with fans about her health battle, revealing she was was diagnosed with Stage 1 Triple Positive Breast Cancer in December but is now "cancer free".

In her post, Kinsey, 53, said she is "so proud" of her friend and said she dealt with the diagnosis with so much "courage and grace".

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"If you are lucky in life, you get a friend that feels like home to you and no matter what comes your way, you feel safe, you feel loved, you feel like everything will be okay. Jenna is that person to me," Kinsey wrote.

Saying she's grateful for their friendship, she wrote: "I am so proud of her. She faced these last months with courage and grace and I have learned so much from her."

She added in part of her post: "I am so happy she is now cancer free and doing so well! Jenna, I love you so much. Always here for you. Side by side."

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Earlier this week, Fischer spoke about her shock diagnosis and said she went through "surgery, chemotherapy and radiation" to combat the disease.

She is is now "cancer free" 10 months on.

"I wanted a photo of myself in my patchy pixie looking happy and healthy to go along with this news," Fischer said in her emotional post.

"Triple positive breast cancer is an aggressive form of breast cancer but it is also highly responsive to treatment," the star explained.

Fischer, who was born Regina Marie Kirk, said she wanted to share her health journey to encourage others to get their breasts checked and keep up-to-date with their mammograms.

"I'm serious, call your doctor right now," she said.

"My tumour was so small it could not be felt on a physical exam. If I had waited six months longer, things could have been much worse. It could have spread."

Fischer celebrated being cancer free by ringing a bell and throwing confetti in the backyard of their home with her family.

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