Response of patients with indolent systemic mastocytosis to tamoxifen citrate

• Tamoxifen administered at 20 mg/day for 1 year was well tolerated.
• No significant reductions occurred in tryptase or bone marrow involvement.
• Alkaline phosphatase, platelets, and urinary N-methylhistamine decreased.
• Urinary 11β-PGF2α excretion and serum LDH increased significantly.

We examined whether tamoxifen citrate at 20 mg/day for 1 year had a beneficial effect on laboratory findings, bone marrow mastocytosis, common clinical symptoms, or quality-of-life assessment for 5 women and 2 men with indolent systemic mastocytosis. Tamoxifen was well tolerated. We found significant reductions in the platelet count, serum alkaline phosphatase, and 24-h urinary excretion of N-methylhistamine and significant increases in serum lactate dehydrogenase and (excluding 2 patients taking aspirin) in 24-h urinary excretion of 11β-prostaglandin F2α. Overall, no change occurred in percent involvement of bone marrow by mastocytosis. Symptom scores were mild and did not change during the treatment. The 36-Item Short Form Health Survey scores for quality of life physical and mental components showed no marked changes. Tamoxifen, an older, nonhematotoxic medication, has limited activity in systemic mastocytosis at the dosage used in this study.