Bone marrow (BM) metastasis from malignant tumors was first reported as a type of ‘diffusely infiltrative carcinoma’ by Jarcho in 1936 (1). In 1979, Hayashi et al defined ‘disseminated carcinomatosis of the BM (DCBM)’ as a clinical entity distinct from the usual types of metastases to the bone and BM. They reported that diffuse infiltrative growth is a characteristic feature of DCBM, and pointed out the association between DCBM and systemic hematological disorders such as hematocytopenia, disseminated intravascular coagulation and microangiopathic hemolytic anemia (2). DCBM may also be referred to as ‘symptomatic BM metastasis’ (3) or ‘BM carcinomatosis’ (4); however, DCBM is considered to be the most appropriate term, as it suggests the diffuse infiltration of the BM by cancer cells and is associated with clinically important hematological disorders. Previous studies have reported that BM metastases from solid tumors are frequently detected in patients with breast, stomach, lung and prostate cancers (2,5–7).

Occult cancer cells in the BM have been reported to occur frequently, even in patients with early-stage breast cancer; however, whether the presence of isolated tumor cells in the BM has prognostic significance remains controversial (8–13). Furthermore, the association between isolated tumor cells in the BM and clinically symptomatic BM metastasis has not been fully elucidated (11,14), whereas clinically evident BM metastasis is relatively common and often progresses to DCBM in patients with metastatic or recurrent breast cancer. It was reported that BM metastases were identified in 6–79% of breast cancer patients at autopsy (15–17), and 27% of autopsy cases were clinically diagnosed with BM metastases prior to autopsy (15). When metastasis to the BM progresses to DCBM, a hematological disorder, such as hematocytopenia, is manifested (4). Therefore, prompt diagnosis and treatment are required to prevent the development of a life-threatening hematological disorder. The aim of the present study was to review the clinical characteristics and treatments of DCBM in breast cancer patients.

The clinicopathological data from two literature reports and our breast cancer cases with DCBM were reviewed (Table III) (3,4). To the best of our knowledge, no clinicopathological characteristics of breast cancer, apart from advanced clinical stage, have been identified as risk factors for the development of DCBM in published reports (3). Clinically, it is important to suspect DCBM when a patient with advanced breast cancer manifests a hematological disorder, such as anemia or thrombocytopenia. Diagnostic tools, such as ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography and blood smear examination have been proposed for the diagnosis of DCBM (18–20); however, examination of a BM biopsy and/or aspirate remains the gold standard (3,14). Pathologically, DCBM is characterized by the diffuse infiltrative growth of tumor cells in the BM, and normal components, apart from bone trabeculae, are largely replaced by the tumor infiltrate (Fig. 2). BM biopsy is considered to be crucial for the accurate diagnosis of DCBM, and is also very important for deciding on a treatment regimen. Genetic heterogeneity of primary and metastatic tumors was recently reported (21–23), and there have been several reports on immunochemical discordance between primary breast cancer tumors and metastatic lesions (24–27). Clinically, the histopathological confirmation of metastatic tissue should be performed whenever possible, due to the potential discordance between the expression status of hormonal receptors and HER2/neu in primary and metastatic breast tumors. Discordant results affect the treatment regimens used for metastatic breast cancer patients (28).

Notably, in all 4 patients, the BM metastatic lesions were negative for progesterone receptor (PgR) expression, whereas the primary lesions of 2 patients (50%) were PgR-positive (Tables I and II). PgR-negative patients with luminal breast cancer are well-known to have a worse prognosis compared with PgR-positive patients (29,30). The PgR expression status has been reported to be frequently discordant between primary and metastatic sites (31–35), and the loss of PgR expression has been associated with worse prognosis due to acquired resistance to hormonal therapy (26,32). The effect of PgR status on DCBM progression is unknown, and additional clinical reviews and molecular studies are warranted.

Prompt systemic treatment is needed for breast cancer patients with DCBM, as DCBM is associated with hematological abnormalities. Among the various treatment regimens for breast cancer, the preferred regimen for DCBM from breast cancer remains unknown. DCBM has been treated by various chemotherapy regimens (Table III) (3,4). Although the therapeutic effects of chemotherapy have not been comprehensively reported, anthracycline and taxane regimens have been more effective compared with other chemotherapy agents. Demir et al reported disease control rates (complete response + partial response + stable disease) of 83% (5/6), 75% (3/4) and 0% (0/3) for anthracycline, taxane and other regimens, respectively (3). Endocrine therapy was administered to 1 patient, who achieved stable disease (3). Based on the patient response to therapy reported previously and observed by us, systemic chemotherapy is recommended for DCBM of breast cancer patients. Endocrine (hormonal) therapy may be added in estrogen receptor-positive cases. Due to myelotoxicity, chemotherapy appears to lead to temporary exacerbation of the hematological disorder, and blood transfusion is often required after the initiation of systemic chemotherapy.

According to previous studies (3,4) and our experience, the median time to DCBM following initial breast cancer diagnosis ranged from 36 to 51 months, and the median survival after diagnosis of DCBM ranged from 6 to 17 months (Table III). Breast cancer patients with DCBM who received systemic chemotherapy were reported to survive significantly longer compared with patients without chemotherapy (3).

The molecular pathogenesis of DCBM in breast cancer is not completely understood. We recently reported that the inhibition of the F-box protein FBXW7 in BM promoted cancer metastasis in mice (36). FBXW7 is a gene that regulates the cell cycle, and it may maintain cancer-initiating cells (37). Despite advances in the understanding of the mechanism and significance of the dissemination of tumor cells in BM, the molecular mechanism underlying the progression of DCBM from a metastasis in the BM remains unknown. The BM environment is considered to have unique biological properties for the homing, survival and proliferation of circulating tumor cells (38). DCBM is considered to progress from BM micrometastases, but further studies are required to elucidate the mechanism of DCBM development in breast cancer patients.

In conclusion, DCBM is a type of metastasis that is characterized by diffuse infiltrative growth, and is associated with poor prognosis and hematological disorders in patients with advanced breast cancer. A definitive diagnosis by BM biopsy and prompt systematic therapy may prolong patient survival.