"Joni is to undergo several more tests, followed by surgery within the week," reported Doug Mazza, president and COO of the International Disability Center of Tada's Joni and Friends ministry.
"The extent of the cancer will not be determined until the procedure," he added.
Tada and her husband, Ken, meanwhile, affirmed their faith in God and said doctors had sought to assure them by telling them that more advancements had been made in the last five years in treating breast cancer then in the last 150 years.
"[A]lthough cancer is something new, I am content to receive from God whatever He deems fit for me," said Tada, who has been a quadriplegic for more than 40 years.
"Yes, it's alarming, but rest assured that Ken and I are utterly convinced that God is going to use this to stretch our faith, brighten our hope and strengthen our witness to others," she added.
As founder of Joni and Friends, Tada has been a strong advocate for people with disabilities. She is senior associate for disability concerns for the Lausanne Committee for World Evangelisation and serves in an advisory capacity to the American Leprosy Mission, the National Institute on Learning Disabilities, as well as on the boards of reference for the Christian Writers' Guild and the Christian Medical and Dental Society.
Her ministry's International Disability Center, meanwhile, serves the disability community by offering a wide array of life-affirming ministries to people with disabilities around the world, including international radio and television programmes featuring inspirational stories.
"We've always prized the ministry God has given Joni and Friends to people facing a variety of disabilities; everything from autism to Alzheimer's, from spina bifida to spinal cord injury," commented Tada, who said she had hoped for years that her quadriplegia might encourage people struggling with cancer.
"[N]ow I have a chance to truly empathise and journey alongside, affirming that God's grace is always sufficient for whatever the disease or disability," she added.
According to Tada's ministry, updates regarding Tada's health and progress will be posted to the "Joni's Corner" section of the Joni and Friends ministry website at www.joniandfriends.org, where well-wishers are invited to post assurances of their prayers and encouragement to Tada and her husband.
Following surgery, Tada will receive treatment based on the findings.
"We are confident Joni is in very good hands," commented Ken, Tada's husband of nearly 28 years.
In addition to the International Disability Center, Joni and Friends also has its Christian Institute on Disability, which equips the Christian community to engage in bioethics and value of life issues.
The Joni and Friends International Disability Center, based in Agoura Hills, California, celebrated its 30th anniversary last year.