Diagnosis of a previously unidentified primary site in patients with spinal metastasis: diagnostic usefulness of laboratory analysis, CT scanning and CT-guided biopsy.

When the primary site is unknown in patients with spinal metastases, there can be problems in locating the site of tumor origin. Most previous reports on metastases of unknown origin have not been limited to the spine. The purpose of this study is to assess the usefulness of laboratory analysis, chest, abdominal and pelvic CT and CT-guided biopsy in patients with spinal metastases of unknown origin (SMUO). A retrospective review of the clinical histories of 27 patients with SMUO was done. A total of 43 patients with SMUO were seen at our institution between 2002 and 2007. Of the 43 patients, 27 who underwent all 3 tests (laboratory analysis including M protein and tumor markers, chest, abdominal and pelvic CT and CT-guided biopsy) were included in this study. We retrospectively assessed the diagnostic usefulness of those 3 tests in the 27 patients. In 27 patients, the final diagnosis was obtained in 26 patients. Myeloma was the most common malignancy followed by lung carcinoma. M protein was positive in all 7 patients with myeloma and negative in patients with other malignancies. The level of tumor markers was elevated in 16 of 17 patients with a solid tumor and in all 3 with lymphoma. CA15-3 was elevated in 4 of 27 patients, CA19-9 in 5 of 27 patients, CA125 in 2 of 27 patients, CEA in 6 of 27 patients, SCC in 2 of 27 patients, NSE in 7 of 27 patients, AFP in 1 of 27 patients, PIVKA-II in 1 of 27 patients, TPA in 6 of 27 patients, IAP in 3 of 12 patients, thyroglobulin in 2 of 27 patients, sIL-2R in 3 of 24 patients, and PSA in 5 of 17 male patients. Myeloma, lymphoma and prostate carcinoma had a marker with high sensitivity and specificity (M protein, sIL-2R and PSA). Eleven primary tumor sites (40.7%) were detected (6 lung, 1 prostate, 1 kidney, 1 thyroid, 1 liver, and 1 pancreas) by chest, abdominal and CT scanning. Biopsy led to determination of the final diagnosis in 12 (44.4%) of 27 patients (5 myelomas, 3 lymphomas, 2 prostate carcinomas, 1 renal-cell carcinoma, 1 thyroid carcinoma). In the remaining 15 patients, biopsy did not lead to determination of the final diagnosis, because the histological diagnosis was either an adenocarcinoma or an undifferentiated carcinoma, the tissue sample was not diagnostic. A laboratory analysis limited to specific tumor markers such as PSA and protein electrophoresis is considered to be useful in making a final diagnosis. Chest, abdominal and pelvic CT is considered to be useful for making a final diagnosis in solid tumors, but not for hematologic tumors. A CT-guided biopsy had a low determination rate in the final diagnosis in comparison to a laboratory analysis and CT scanning for solid tumors and it is not considered to be essential for the diagnosis of hematologic tumors.