Intriguingly, whereas MEK inhibitors do not alter ALC, among BRAF inhibitor treatments, vemurafenib [105] but not dabrafenib [105, 106] induces lymphopenia affecting principally CD4+ T cells that may either result from a change in their compartmental distribution in the tumor [107] or secondary lymphoid tissue or from an absolute lymphopenia due to direct effect of BRAF inhibition on T cells. The gene discussed is BRAF; the disease is lymphopenia.