Comparison between solitary and multiple skeletal metastatic lesions of breast cancer patients

Background: Breast cancer has been the subject of many recent studies because it is a significant cause of death in women. This study was performed to clarify whether solitary skeletal metastasis has clinical significance compared with multiple skeletal metastasis. Patients and methods: Seven hundred and three patients who developed metastatic bone lesions up to September 2002 after beginning treatment for breast cancer from 1988 to 1998 were included. The lesions were classified first as solitary or multiple based on bone scan results and then according to anatomical distribution. Next, solitary-to-multiple conversion was investigated in patients with solitary skeletal metastasis. Then factors related to solitary or multiple skeletal metastasis were analyzed. The prognosis of skeletal metastasis was compared between patients with solitary or multiple metastatic bone lesions. A Cox proportional hazards model was used to test whether solitary skeletal metastasis compared with multiple skeletal metastasis was an independent factor of survival. Results: Two hundred and eighty-nine patients (41%) had solitary skeletal metastasis and 414 patients (59%) showed multiple skeletal metastasis. The sternum was a frequent site for solitary skeletal metastasis (98 of 289, 34%), while other skeletal sites were more frequent in patients with multiple metastatic bone lesions (P <0.001). Solitary sternal metastatic lesions remained solitary longer than solitary metastatic bone lesions to places other than the sternum (P <0.001), but did not lengthen patient survival times (P = 0.871). The factors related to solitary skeletal metastasis are TNM stage (tumor-node-metastasis) and histology. The patients with earlier stage and favorable histology tend to have solitary skeletal metastasis. The patients with solitary skeletal metastasis lived longer than those with multiple metastatic bone lesions (P <0.001). Multivariate analysis revealed that a solitary metastatic bone lesion (P = 0.002) is an independent favorable prognostic factor in patients with skeletal metastasis. Conclusions: Solitary skeletal metastasis has a different anatomical distribution and is an independent prognostic factor in patients with skeletal metastasis.