Bone is the third site of metastasis of cancer after the liver and lungs. This underpins that the bone is a good “soil” for the “seed” tumor. The inaugural metastases are common and represent 22.6% to 30% of bone metastases [1] -[3] . The primary focus of these metastases is often the prostate, breast, kidney, lung and thyroid. Cancers of the five foci represent between 80% and 96% of cancers responsible bone metastases [2] -[5] .

The recognition of a secondary bone tumor based on the comparison of epidemiological, clinical, radiological and pathological. Imaging of bone tumors remains dominated by X-ray.

Their treatment requires a multidisciplinary approach. Radiation therapy is one of the key resources available to treat bone metastases near all medical or surgical arsenals [4] . According to Conroy, the median survival of bone cancer is five months after diagnosis with 5% at five-year survival and 1% at ten-year survival [3] . Many African studies have discussed the issue as reflected the recently published [6] -[11] . In Benin, no study has been done on bone metastases. The objective of this study was to clarify the epidemiological, diagnostic and therapeutic aspects of bone metastases in the Rheumatology Department of the National Hospital University Hubert Koutoukou Maga of Cotonou.

It was a descriptive and retrospective cross-sectional study, carried out over 15 years from 1999 to December 2013 on the records of patients treated in the rheumatology department. Patients met the following criteria:

・ Have consulted or been hospitalized in the rheumatology department during the study period;

・ Have presented an inflammatory bone pain or pathological fracture of long or flat bones or bone swelling related to a secondary bone cancer.

The diagnosis of secondary bone cancer was confirmed after a bone biopsy or the discovery of a primitive cancer.

Patients with hematologic malignancy or with incomplete or insufficiently explored records were excluded from the study.

Variables evaluated were: socio-demographic (age, sex), therapeutic itinerary, cliniac features (pain, fever, lameness), radiological, etiological and therapeutic parameters. The statistical analysis of results was performed using Epi info 7.0 software and STATA/IC 11.0.

This investigation was approved by the local Ethics Committee.

Although Tubiana-Hulin has reported that bone metastases accounted for over 90% of malignant disease of the bone [5] , they are relatively rare in our series (51 patients had bone metastases over 15 years) and other African series like the recently published works (77 cases in 19 years in Togo and 81 cases in 7 years in Congo) [6] [7] . The frequency of bone metastases is certainly underestimated in the world. Indeed, some post-mortem series seeking to determine the prevalence of bone metastases at death revealed it can reach up to 73% [5] . Male predominance has been reported by the same authors in their series. This dominance is classic as described by many authors [8] -[12] . It seems to be explained by the frequency of prostate cancer which diagnosis is easy in our professional context [13] [14] .

The mean age of patients was 54 ± 9 [26 - 85] years. These data were found in African work such as Kouakou in Cote d’Ivoire in 1994 [15] , Ntsiba in Congo in 2013 [7] and Oniankitan in Lome in 2014 [6] . Bone metastases appear later in the Western series represented by Houze et al. and Vandecandelaere et al. who reported 77 and 63 years old for mean age of their patients respectively [14] [16] .

Clinically, the main symptom was inflammatory bone pain. For Ntsiba et al. bone pain was the main mode of discovery of metastases (67.9% of cases), followed by neurological manifestations compression (17.1%) [7] . Oniankitan et al. [6] meanwhile, found themselves bone inflammatory pain (76.6%), impaired general condition (75.3%) and the compression of the spinal cord (34 cases; 44.1%).

In X-rays, radiological lesions were usually multiple with an equal proportion of osteoblastic and osteolytic lesions. These lesions mainly sit on pelvis, spine and femur. This distribution of the lesions was found by Oniankitan [6] . The achievement of the long bones was present in 18.2% of their patients. The same observations were made in the series of Ntsiba with a majority reached at the lumbar spine (33.3%), femur (19.0%) and pelvis (14.3%) [7] . These African data are similar to those published by other Maghrebian and Western authors [12] [16] . This appears as geographic distribution in the case of prostate cancer. Prostate is located in the pelvis and its cancer metastasis in pelvis, thoracolumbar spine and the femur. On the other side, the geographical distribution is less obvious in breast cancer cases. However, the extraordinary mass and exchange surface that forms the spine appears to be one explanation for the preponderance of spinal disease [16] .

The distribution of the primay cancer is the same as African [6] -[12] and Western series [5] [16] . It was unknown in 1.9% of cases in our series unlike the Ntsiba where it was 6.2% [7] .

The occurrence of bone metastases was relatively frequent in carcinomas of the prostate, breast and stomach. In our country, a good physical examination of the patient combined with radiological images allows referral to the primary tumor.