Hiding in the Kidney: A Series of 13 Lymphoid Proliferations Clinically Mimicking Renal Carcinoma

In the clinic, we often encounter renal masses as presumptive carcinomas originating from genitourinary tissue, and they are diagnosed and treated as such. However, as our study of 13 patients demonstrates, they are not always what they seem.

The lesions we describe, ranging from benign phenomena such as IgG4-related disease and reactive follicular hyperplasia to malignancies such as indolent marginal zone lymphomas to aggressive, diffuse large B cell lymphomas, highlight a potential critical diagnostic blind spot. Despite presentations with symptoms and imaging suggesting most likely renal carcinoma, including hematuria and flank pain, these lesions had entirely different pathobiology and therapeutic implications, including potential systemic neoadjuvant/adjuvant therapies and follow-up neoplastic workup. In some cases, they existed as part of collision tumors with renal cell carcinoma.

Importantly, the diagnoses in these patients were generally made post-nephrectomy after initial suspicion of the existence of a carcinoma; this raises the question of whether more precise pre-operative diagnoses can be made to avoid unnecessary nephrectomies. More advanced imaging modalities, percutaneous biopsy, and interdisciplinary discussion may help in this regard. Though these lymphoid-origin lesions are uncommon, they are not exceedingly rare and should be considered when working up a renal mass. The genitourinary system also provides a unique solid tissue microenvironment in which cells of hematolymphoid origin may be steered to reactive or neoplastic purposes, and further understanding of this setting should help determine the exact factors that may make these lesions more likely in some patients.

Written by: Jihoon William Lee, MD, PhD, Department of Laboratory Medicine and Pathology, Medical Scientist Training Program, University of Washington, Seattle, WA, USA

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