Studies on Tumor Metastasis: V. The Metastases of Carcinoma to the Spleen

During the past few years considerable attention has been given to the spleen and its relation to cancer, with special emphasis on its infrequency as the site of carcinomatous metastases. From the literature, one would conclude that metastatic carcinoma is rare in the spleen and rare out of all proportion to its occurrence in other organs, such as the liver, kidneys and lungs, and that no definite decision has been reached as to why this particular organ should be so infrequently involved. Ewing (1), for example, says: “The spleen, however, seems to escape [metastases] with peculiar frequency.” Stengel and Fox (2) state: “Secondary carcinoma is rare in the spleen.” Beattie and Dickson (3) write: “Metastatic growths of cancer and sarcoma may occur, but, except where its surface is involved as part of a general peritoneal spread, the spleen, as a rule, escapes the presence of metastases, even when these are numerous in other organs.”Statistics by various authors concerning frequency of metastatic carcinoma of the spleen vary considerably, as shown in Table I. It is apparently impossible to explain these variations, but we believe that they may be caused in part by differences in opinion as to when tumor cells present in this organ should be considered metastatic growths. This leads to the question: should small clusters of tumor cells in the blood vessels or sinusoids be considered as metastases? We define a metastatic growth as a non-contiguous secondary nodule of tumor cells. Metastases should not be confused with even the most extensive local invasion. Krumbhaar (9) is of the opinion that the mere presence of tumor cells in the blood stream does not constitute a metastatic growth. Since we do not know of any method whereby we can determine whether or not a particular cluster of tumor cells located in capillaries, sinusoids, or larger vessels, if undisturbed, would continue to grow and invade the adjacent parenchyma, we feel that any cluster of viable tumor cells separated from the primary tumor must be considered as a metastasis. No one would consider a lymph node as free from tumor if its sinuses contained tumor tissue.