Simultaneous Presentation of Breast Cancer and Solitary Rib Plasmacytoma Mimicking Breast Cancer Metastasis: A Report of a Rare Case.

In the realm of oncology, the detection of lytic bone lesions in patients with breast cancer commonly raises suspicions of metastatic disease, due to breast cancer's known propensity to metastasize to bone. However, the clinical journey of diagnosing such lesions demands a discerning differential diagnosis, particularly when encountering rare entities like solitary rib plasmacytoma alongside breast cancer. This case report elucidates the diagnostic challenges and clinical implications of managing a patient with dual malignancies, emphasizing the importance of an exhaustive and nuanced diagnostic approach. It highlights the need to differentiate between metastatic breast cancer and other primary malignancies, such as plasmacytoma, which can critically influence staging, prognosis, and therapeutic strategies. This case report presents a 64-year-old female patient with a diagnosis of breast cancer who was found to have a co-existing rib plasmacytoma and highlights the diagnostic challenges posed by dual malignancies. This patient presented with a single lytic bone lesion in the rib at the time of breast cancer diagnosis and staging workup. Despite initial suspicion of metastatic breast disease, the atypical presentation warranted further investigation. The diagnostic workup revealed a solitary rib plasmacytoma, emphasizing the importance of a comprehensive diagnostic approach. Following confirmation of non-metastatic plasmacytoma, the staging of breast cancer was revised. This case illustrates how breast cancer, being the most common global malignancy, can simultaneously present with other malignancies that can imitate a different cancer staging.