Abstract

Introduction: Cancer of Unknown Primary (CUP) defines those cancers where metastasis is found to be the primary manifestation and extensive imaging and laboratory studies do not reveal the origin of the disease.  Without finding the source of metastatic disease, progression and treatment become murky at best. We hope to highlight a patient’s course from the unknown to diagnosis.

Case Description: This case follows a 68-year-old African American female who presented with worsening chronic lower back pain that was poorly controlled with pain management. After extensive imaging, she was found to have innumerable osseous metastases spanning the entire spinal column. An initial diagnosis of Multiple Spinal and Pelvic Lesions concerning for Metastatic Disease with Unknown Primary was given, and a workup for Multiple Myeloma was started.  

Discussion: Preliminary bone biopsy report of patient’s osteolytic metastases showed plasma cells which lead us to suspect Multiple Myeloma. CA 19-9, CEA, Immunofixation (Urine and Serum), Urine Protein Electrophoresis, and Serum Protein Electrophoresis were collected and returned negative. Final bone biopsy showed hypercellularity containing aggregate nests of atypical mononuclear cells. Immunohistochemistry showed cells positive for AE1/3, GATA3, and ER, indicating possible breast cancer as a primary source. Re-review of patient’s last mammogram, completed 2 months before hospital stay, shows a subtle soft tissue density hidden by heterogeneously dense fibrotic breast tissue.

Conclusion: This report illustrates a case of CUP that was able to be resolved with continuous testing. It is unusual to have such a small lesion lead to such a widespread metastatic disease.