Familial adenomatous polyposis and papillary thyroid cancer
Unlike medullary thyroid cancer, most cases of papillary thyroid cancer are sporadic. However, certain genetic syndromes are associated with increased risk of papillary thyroid cancer.
I recently saw a 35-year-old man with a family history of familial adenomatous polyposis. A 39-year-old brother recently died from metastatic colon cancer. His mother and sister were also afflicted and have had colectomies. The patient himself has not had any colon polyps identified on colonoscopy. He has a multinodular goiter with several subcentimeter nodules. The largest nodule was benign on fine needle aspiration. His history is further complicated by the fact that he had lymphoma in his teens for which he received head and neck irradiation.
His question for me: What is my risk of papillary thyroid cancer?
FAP and related syndromes are due to a germline mutation in the adenomatous polyposis coli gene. In classic FAP, afflicted individuals develop hundreds if not thousands of colon polyps with almost all developing colon cancer by age 35 to 40 if left untreated. There are variants of familial polyposis with fewer polyps and a later presentation.
FAP can be associated with other complications including desmoid tumor, medulloblastoma, hepatoblastoma, thyroid cancer, gastric cancer, pancreatic cancer, osteoma, adrenal malignancy and other tumors. The lifetime risk of papillary thyroid cancer in FAP is generally thought to be only 1-2%. It is more common in women than men. However, one series of women with FAP found a 12% risk of papillary thyroid cancer.
Diagnosis of FAP can be made in individuals with 100 or more colorectal polyps (particularly multiple polyps before age 40) or fewer than 100 polyps with a relative who has FAP. Given that this gentleman does not yet have evidence of colon polyps, more than likely he has not inherited FAP.
Nevertheless, even if he has not inherited FAP, the lifetime risk of thyroid cancer in a multinodular goiter could be as high as 5-7%. His history of head and neck irradiation for lymphoma further increases his risk. Most of this patients thyroid nodules are less than 0.5 cm with reassuringly benign ultrasound characteristics. We will follow him with thyroid ultrasound in the future.
If there is any change in size or other ultrasonographic features of any of these nodules, we would evaluate further with another fine needle aspiration biopsy. If our index of suspicion is high, we may proceed with surgical resection, even if fine needle biopsy is benign. This possibility of missing thyroid cancer in a benign fine needle biopsy is low, less than 1-2%, but it is not zero.