Can I use Mounjaro (tirzepatide) if I have a family history of non-medullary thyroid cancer?

Using Mounjaro (Tirzepatide) with Family History of Non-Medullary Thyroid Cancer

Having a family history of non-medullary thyroid cancer does not contraindicate the use of Mounjaro (tirzepatide). While GLP-1 receptor agonists like tirzepatide have contraindications related to thyroid cancer, these specifically apply to medullary thyroid cancer and MEN2 syndrome, not non-medullary thyroid cancer.

Contraindications for Tirzepatide (Mounjaro)

Absolute Contraindications:

• Personal history of medullary thyroid carcinoma (MTC)
• Family history of medullary thyroid carcinoma (MTC)
• Multiple endocrine neoplasia syndrome type 2 (MEN2) 1, 2

Important Distinction:

• Non-medullary thyroid cancer (which includes papillary and follicular types) is distinct from medullary thyroid cancer
• The contraindication is specific to medullary thyroid cancer, not all thyroid cancers 2

Scientific Rationale

The contraindication for medullary thyroid cancer is based on:

• Animal studies showing increased risk of thyroid C-cell tumors with GLP-1 receptor agonists
• C-cells are the cells that develop into medullary thyroid cancer
• Non-medullary thyroid cancers arise from follicular cells, not C-cells 1, 2

Risk Assessment for Non-Medullary Thyroid Cancer

Familial non-medullary thyroid cancer (FNMTC):

• Represents approximately 5-10% of all thyroid cancers 3, 4
• Defined as two or more first-degree relatives with non-medullary thyroid cancer 3
• Has different genetic mechanisms than medullary thyroid cancer 1
• Not associated with the RET gene mutations that cause MEN2 and medullary thyroid cancer 1

Monitoring Considerations

If you decide to use Mounjaro with a family history of non-medullary thyroid cancer:

• Monitor thyroid function if you are on levothyroxine, as semaglutide (a similar GLP-1 RA) has been reported to affect thyroid function in some cases 2
• Be aware of symptoms that would warrant evaluation (neck mass, dysphagia, hoarseness, persistent cough)
• No special thyroid cancer screening is recommended solely based on GLP-1 RA use 2

Clinical Decision Algorithm

1. Confirm the type of thyroid cancer in family history

   • If medullary thyroid cancer → DO NOT use Mounjaro
   • If non-medullary thyroid cancer → Can use Mounjaro

2. Assess for other contraindications to Mounjaro

   • Personal history of pancreatitis
   • Hypersensitivity to tirzepatide

3. Consider benefit-risk profile

   • Weigh metabolic benefits against theoretical concerns
   • Consider cardiovascular and weight management benefits

Pitfalls to Avoid

• Don't confuse non-medullary thyroid cancer with medullary thyroid cancer
• Don't unnecessarily withhold beneficial therapy based on unrelated cancer history
• Don't order unnecessary thyroid cancer screening solely due to GLP-1 RA use
• Don't overlook the need for monitoring thyroid function if the patient is on thyroid medication

In conclusion, a family history of non-medullary thyroid cancer is not a contraindication for using Mounjaro (tirzepatide). The specific contraindication applies only to medullary thyroid cancer and MEN2 syndrome.