Complex sentence: The chances of them contracting cancer is extremely high, especially thyroid cancer, so much so that the scar on the neck after an operation for the thyroid is known as the 'Belarussian Necklace.
Split into simpler sentences: The chances of them contracting cancer is extremely high, especially thyroid cancer. So much so that the scar on the neck after an operation for the thyroid is known as the 'Belarussian Necklace.