Estrogen is involved in hemangioma regression associated with mast cells

BACKGROUND: Estrogen plays a role in infantile hemangioma (IH) development, but the underlying mechanism remains unclear. This study aimed to assess estrogen and estrogen receptor (ER) localization and expression levels in IH. In addition, the unexpected relationship between mast cells (MCs) and estrogen in human IH was discussed. METHODS: IH (n = 29), vascular malformation (VMs, n = 33) and normal skin (n = 15) specimens were assessed. IH was classified into proliferative (n = 9; age, 3.56 ± 1.01 months), early involuting (n = 10; age, 8.90 ± 2.69 months) and late involuting (n = 10; age, 20.10 ± 4.93 months) groups. Estradiol (E2), ER-a, ER-β, and tryptase (MC marker) levels were determined immunohistochemically and/or by double immunofluorescence staining. Quantification and localization of tryptase, ER-a, and E2 were assessed for each specimen. RESULTS: ER-a, E2, and tryptase were expressed in the cytoplasm and nucleus of MCs in IH. The IH specimens showed significantly more tryptase, ER-a, and E2 positive MCs (30.6 ± 12.7, 9.7 ± 5.6, and 19.8 ± 8.7 cells/high-power field [HPF], respectively) compared with VM specimens (9.0 ± 9.8, 1.5 ± 2.4, and 2.5 ± 4.1 cells/HPF, respectively) and normal skin (6.1 ± 8.5, 0.5 ± 1.2, and 1.9 ± 3.4 cells/HPF, respectively). Proliferating IH displayed fewer E2 positive MCs (14.0 6.3 cells/HPF) compared with early (22.3 ± 10.2 cells/HPF, P = 0.023) and late (22.4 ± 6.8 cells/HPF, P = 0.006) involuting specimens. In addition, proliferating IH showed fewer tryptase positive MCs (24.7 ± 10.8 cells/HPF) compared with early involuting specimens (35.7 ± 15.3 cells/HPF, P = 0.043). All IH specimens were ER-a positive and ER-β negative. CONCLUSIONS: E2 and ER-a are expressed on MCs and not on IH endothelial cells. Furthermore, activated MCs may be involved in IH regression.