CD44 and cancer: Initial characterization of the isolated CSCs, revealed a high expression of the cancer stem cell marker CD44, which is known to mediate cancer cell survival, proliferation and motility, as well as the modulation of tumor microenvironment.[31,32] Moreover, it is known that CD44 expression is dominant within pulmonary carcinoids, decreasing from TC to AC to very low levels in LCNEC and SCLC,[33,34] which stands in line with the presented data.