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Chicago, Jan. 4, 1907.
To the Editor:
—The zealous search for a parasite in cancer tends to obscure the obvious phyletic factor, illustrated in its distribution and clinical course.The oldest of the three embryonic layers (epiblast) produces the epithelium of the skin, the central nervous system, and later the anus. The second layer (hypoblast) produces the epithelium of the alimentary canal and associated glands. The last and intermediate layers (mesoblast) produce the connective-tissue structures and the reproductive organs. The mesoblastic tissues complete their development after puberty.The malignancy and frequency of cancer seem to vary directly with the phyletic age of the various organs, being least in the earliest, greatest in the latest organs. Thus carcinoma is notoriously frequent and malignant in the breast and uterus. The breast, a specialized skin gland, appears with the mammals; the completely fused uterus with specialized cervix appears in the apes—both therefore among
Belfield. WT. The Phyletic Factor in Cancer.. JAMA. 1907;XLVIII(3):242–243. doi:10.1001/jama.1907.02520290058014