Inclusion Criteria:

- Histologically confirmed MTC with signs of residual/persistent disease based on tumor
marker levels and/or radiographic imaging. Pathologic diagnosis must be confirmed at
UWCCC. Grading must be confirmed by pathologic review performed at UWCCC.

- Elevated neuroendocrine markers at least 1 month post -op. In MTC, persistently
elevated neuroendocrine markers such as calcitonin and CEA are indicative of
persistent disease.

- Disease progression is not required for this trial

- 4 weeks from the completion of major surgery, chemotherapy, or other systemic
therapy or local liver therapy to study registration. Subjects will have had
standard of care prior to enrollment. Subjects will have had standard of care
prior to enrollment (for example it could include total thyroidectomy, central
lymph node dissection, and when necessary ipsilateral radical neck dissection
but is tailored to the patient).

- 3 weeks from the completion of radiation therapy to study registration

- The following laboratory values obtained within 14 days prior to registration:

- Absolute neutrophils count (ANC) ≥ 1000/mm3

- Platelets ≥ 75,000/mm3

- Hemoglobin ≥ 8.0 g/dL

- Total bilirubin greater than or equal to 2.0 X the upper limit of normal (ULN)

- AST greater than or equal to 3 X ULN or greater than or equal to 5 X ULN if
liver metastases are present

- Creatinine greater than or equal to ULN

- Serum sodium within normal limits

- ECOG performance status of 2

- Capable of understanding the investigational nature, potential risks and benefits of
the study, and able to provide valid informed consent.

- Availability of tissue specimens to be analyzed for pathologic confirmation.

- Age ≥ 18 years.

- Women must not be pregnant or lactating due to the deleterious effects of Lithium
carbonate on a fetus or small child. All females of childbearing potential must have
a blood test or urine study within 2 weeks prior to registration to rule out
pregnancy.

- Women of childbearing potential and sexually active males are required to use an
accepted and effective method of contraception.

- Patients must not have known history of allergic reactions or adverse reactions to
Lithium or its derivatives.

- Patients are not allowed to be on concurrent chemotherapy or radiation therapy.

Exclusion Criteria:

- Gastrointestinal tract disease resulting in an inability to take oral medication
(i.e. ulcerative disease, uncontrolled nausea, vomiting, diarrhea, bowel obstruction,
or inability to swallow the tablets).

- Significant, active cardiac disease

- Patients must not be taking the following medications: diuretics, ACE inhibitors,
NSAIDs (except aspirin or sulindac), neuroleptics, tetracycline, and COX2 inhibitors.

- Patients with radiographic evidence of disease will be presented the option to
undergo a tumor biopsy although this is not mandatory.

- Patients already taking Lithium for any reason are not allowed on study