Certain cases of depletion of red blood corpuscles are usually classified as secondary or symptomatic anemia. The blood picture is characteristic and the disease condition associated with it is usually relatively mild, though there are exceptions to this rule. Both hemorrhage and hemolysis may be responsible for secondary anemias; but Richard Cabot has well stated that the presence of a clear cause remains the only reliable criterion for the recognition of the secondary type. Cancer has long been known to be responsible for secondary anemias. The origin of the hemorrhages produced by neoplasms along the alimentary tract is obvious. From the standpoint of their persistence and the intensity of the blood changes, certain long recognized features have been difficult to interpret.
Attention has long since been called to the fact that carcinoma of the proximal half of the colon has a greater tendency to the production of anemia than carcinoma
CARCINOMA AND ANEMIA. JAMA. 1927;89(19):1610. doi:10.1001/jama.1927.02690190048017