The distribution of cutaneous metastases correlates with local immunologic milieu

Background: Metastases to the skin are found with increased frequency at certain sites, such as the scalp, but the biological factors that influence this distribution are not understood.

Objective: We aimed to compare the proportional frequency of metastases at various cutaneous locations with the immunologic microenvironments at those sites.

Methods: We retrospectively identified all biopsy specimens of cutaneous metastases diagnosed at our institution from 1991 to 2014 (n = 1984) and mapped their anatomic distribution while controlling for regional surface area. Using a separate, mapped cohort of normal-appearing skin samples (n = 140), we measured the density of regulatory T cells, CD4(+) effector T cells, and CD8(+) T cells by flow cytometry.

Results: Per unit surface area, cutaneous metastases arise most commonly on the head and neck, followed by the trunk, upper extremities, and lower extremities, respectively. Sites with more frequent metastases tend to contain a greater density of regulatory T cells and a lower proportion of CD8(+) T cells (P < .05).

Limitations: Immunologic factors were only assessed in control tissue and were not measured from patients with metastatic disease in this correlative single-center study.

Conclusion: The distribution of cutaneous metastases follows the distribution of regulatory and effector T cells in skin. Further studies are required to prove a mechanistic association between local immunologic factors and the development of cutaneous metastases.