The Ultimo bra tycoon said her actions had left her "petrified" that she had contracted the disease.
The 41-year-old, who has worked with cancer charities which urge women to take decisive action to prevent cancer, said she had shocked herself by failing to follow it up earlier.
Mone was eventually treated at the London Breast Clinic.
She wrote on Facebook: "I help so many breast cancer charities so it's shocking how I ignored a lump for six months. Like many I was petrified. Results back today ... all clear and very healthy breasts.
"Reason for this message is girls please don't do what I did and ignore it.
"Act fast and always check your breasts. I can't describe the feeling of fear but saying that I am please to have experienced so I can help more."
Mone has recently gone through a divorce from her husband Michael Mone, who co-founded her bra empire. She underwent surgery to remove a cancerous mole from her shoulder last year.
Breast lumps are one of the main indications of the disease and doctors say that early diagnosis and treatment vastly increase sufferers' chances of survival.
More than 45,500 cases of breast cancer are diagnosed annually in the UK.