Is the spleen able to prohibit tumor cell proliferation?

Primary and metastatic tumors of the spleen are described as unusual, excluding involvement by lymphoma.

Indeed, isolated splenic metastasis from colorectal carcinoma is not a common occurrence. Its rareness has been hypothetically explained by several characteristics of the spleen, such as anatomical, histological and immunological features.

One case of isolated splenic metastasis from colonic carcinoma with a concomitant splenic abscess conducted by the research group of Dr. Adolfo Pisanu from Universit¨¤ degli Studi di Cagliari has been recently reported in the November 7 issue of the World Journal of Gastroenterology because of the interesting characteristics of this rare clinical entity.

Surprisingly, only 41 cases of isolated splenic metastasis from colonic carcinoma have been reported in the world literature. The rareness of splenic metastasis arising from colonic carcinoma suggests the existence of some mechanism that prohibits tumor cell proliferation in the spleen.

Anatomical and immunological characteristics may be reasons for the rarity of isolated splenic metastasis. Because the spleen is the second largest organ of the immunological system, immune surveillance appears to potently inhibit tumor cell proliferation. Moreover, experimental studies have shown that the growth rate of cancer cells injected into the spleen is significantly lower than that of the same cells injected into the liver.

The diagnosis of isolated splenic metastasis is generally made by imaging studies during the diagnostic evaluation of a colonic cancer. Only a few patients with splenic metastasis become symptomatic because of the presence of an associated splenic abscess or spontaneous rupture of the spleen.

When colorectal cancer is suspected, careful examination of the abdominal CT scan can allow early diagnosis of a splenic involvement by the tumor. Clinicians must pay close attention to the spleen for the early diagnosis of isolated splenic metastasis when routinely evaluating abdominal CT scan and abdominal ultrasonography following surgery for colorectal cancer.

Splenectomy followed by chemotherapy seems to be the preferred treatment of isolated splenic metastases from colorectal carcinoma. Literature review suggests there might be a significant improvement of long-term survival following splenectomy for metachronous splenic metastasis from colonic carcinoma. Nevertheless, prognosis for synchronous splenic metastasis seems to be related to the advanced stage of the disease.

Finally, the spleen is considered unfavorable to the development of metastases but the reason for this is not clearly understood. Following the small number of cases reported in the literature, no definitive conclusions can be drawn. Therefore, the researchers are looking forward to new studies to elucidate this issue.