[en] The cause of malignant involvement of the sternum is thought to be hematogenous seeding as well as direct invasion from parasternal lymph node metastasis. The purpose of this study was to examine the pattern of metastasis to the sternum in patients with breast cancer and to evaluate the usefulness of postoperative irradiation for controlling sternal metastasis. Of 306 consecutive cases that were retrospectively reviewed, 16 (5.2%) were found to have sternal metastasis. Six cases had only the sternal lesion as the initial site of bone metastasis, and the others had a sternal lesion as part of multiple metastases. Three of 5 cases with a solitary sternal lesion were found by follow-up bone scintigraphy to have expanded to multiple bone metastases. The incidence of sternal metastases in patients with postoperative irradiation was significantly lower than that in nonirradiated patients (p<0.001). Although the incidence of sternal involvement in patients with breast cancer was not low, it might be diminished by postoperative irradiation. (author)