Metastatic bone cancer as a recurrence of early gastric cancer -- characteristics and possible mechanisms.

The surgical outcome of most early gastric cancer (EGC) is usually satisfactory. Some cases show bone metastasis even though the depth of cancer invasion is confined to the mucosa. The most frequent site for recurrence of EGC is the liver. Cases of EGC with bone metastasis are reviewed to clarify the clinicopathological characteristics of EGC giving rise to bone metastasis. Possible mechanisms and risk factors underlying this rare condition are proposed. Forty-six cases of bone metastasis from EGC are reviewed from published reports and meeting proceedings in Japan. This investigation suggests that risk factors for bone metastasis from EGC include depressed-type signet-ring cell carcinoma, poorly differentiated carcinoma, and/or the likely involvement of lymph node metastasis, even though the cancer is confined to the gastric mucosa. The risk factors do not include recurrence of EGC in the liver. We speculate that the mechanism of bone metastasis from EGC is via lymphatic channels and systemic circulation. Post-operative follow-up of cases should consider the development of bone metastasis from EGC. We propose the use of elevated alkaline phosphatase levels for the detection of bone metastasis and recommend bone scintigraphy in positive cases.