Rapidly progressive malignant pelvic Perivascular Epithelioid Cell Neoplasm (PEComa) associated with Eggerthella lenta Bloodstream Infection.

Perivascular epithelioid cell tumors (PEComa) are rare mesenchymal neoplasms composed of cells that express melanocytic and myogenic markers and grow around small blood vessels. PEComa often show benign behaviors but can also be highly aggressive. In frail and more complex patients, many conditions can overlap, compounding the diagnostic and therapeutic difficulties inherent in rare diseases. Moreover, the complexity of modern patients introduces new and significant players in host-microbe interactions, and emerging pathogens represent a relevant challenge to modern healthcare. Among these pathogens is Eggerthella lenta, an anaerobic gram-positive bacterium of the normal gut microbiota associated with life-threatening infections. Here, we present a case of malignant pelvic PEComa with rapid metastatic progression in a 73-year-old man who presented with an E. lenta bloodstream infection. Approaching differential diagnosis with open-mindedness may assist in better imaging interpretation, surgery scheduling, and proper treatment planning. The non-specific clinical presentation might delay timely diagnosis, while the absence of well-consolidated guidelines undermines the accurate management of the disease, for which strict follow-up can favor better outcomes. Progress in diagnostic techniques, such as the implementation of matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry for microorganism identification, helps with a more accurate pathogen diagnosis and characterization. This allows the implementation of the most appropriate therapy, as well as better surveillance of antibiotic resistance, infection prevention, and control measures. Nevertheless, a good dose of wisdom is vital to avoid overlooking potentially harmful pathogens, particularly in frail individuals.