The 15 hikers have raised almost £9,000 ahead of their challenge on Saturday, June 11, which starts at Brighton Racecourse and ends at Helen Garden in Eastbourne.
The walk is in honour of company director Jackie Johanson from Hassocks.
Jackie, 53, is undergoing chemotherapy after being diagnosed with breast cancer. She is set to have a mastectomy in June.
She said: “In November 2021 I found a lump in my breast and was referred by my GP to the wonderful Park Centre for Breast Care in Brighton.”
After mammograms, ultrasounds and biopsies she was told she had breast cancer on December 8 in three areas and in her lymph nodes.
Jackie lives with her husband Tony, who is also company director, and their three daughters Amy, Jodie and Hannah.
She said she is proud of her colleagues for walking this ‘mighty hike’.
“We are a small family business with a dedicated, hardworking team and I know they’ll smash it,” she said.
Jackie urged others to check for any changes in their breasts.
She said: “I never thought this would happen to me. Even after I found the lump, I thought it would end up being nothing. I am so very grateful for the support and treatment I have received from Macmillan and also the NHS.”
Jo Gimson from H&D Air Conditioning said the team wanted to help both Jackie and MacMillan Cancer Support who do ‘a wonderful job’ supporting cancer patients through treatment.
Jo, 51, lives in Burgess Hill with her husband Matt and their westie dog Molly and said her training involves running, weightlifting, cycling and regular walks.
She said: “Most of us from H&D Air Conditioning have never walked this far before so the training is gruelling, however it’s nothing in comparison with the treatment cancer patients have to go through.”
Jo said she is looking forward to the walk and seeing others taking part.
"It will be emotional and hard but with all of us behind each other we will do it.”