Which lymph nodes are most likely to be involved in the metastasis of a tumor from the skin over the xiphoid process?

The correct answer is D.

The skin over the xiphoid process is located in the upper anterior trunk, above the level of the umbilicus. Lymphatic drainage from the skin of the trunk above the umbilicus primarily drains to the axillary lymph nodes. Therefore, these nodes would be most likely to be involved in the metastasis of a tumor from this area.