Cutaneous Lymphoma or Not? Clonality as a Helpful Adjunct

The discussion primarily revolves around the role of clonality studies in diagnosing cutaneous lymphoma, specifically mycosis fungoides (MF). The speaker introduces a case of a patient with a history of MF who developed a new rash following treatment, raising questions about treatment efficacy and potential disease progression. The case highlights the importance of immunostains, specifically CD3 and CD8, in examining tissue samples. The presentation emphasizes the difference between PCR and next-generation sequencing (NGS) for clonality studies, noting that while PCR is more widely used, NGS offers superior sensitivity and specificity in detecting monoclonality associated with malignancies. Common misconceptions about clonality are addressed, clarifying that clonality does not equate to malignancy and that benign inflammatory conditions can also present clonally. The speaker describes the mechanics of T-cell receptor gene rearrangement relevant to clonality assessment and details the processes involved in both PCR and NGS approaches. While PCR is effective, it's limited by interobserver variability and reduced sensitivity in early-stage disease. In contrast, NGS, while more complex and expensive, enables better tracking of clonal evolution over time and is effective in predicting disease progression. Ultimately, both methods serve as adjuncts, reinforcing the need for a comprehensive clinical and histopathological evaluation in diagnosing cutaneous lymphomas.