Primary mediastinal large B-cell lymphoma, classic Hodgkin lymphoma presenting in the mediastinum, and mediastinal gray zone lymphoma: what is the oncologist to do?

In recent years, an overlap in biologic and clinical features has been identified between classic Hodgkin lymphoma (CHL) and primary mediastinal large B-cell lymphoma (PMBL). Further strengthening this relationship is the identification of lymphomas with clinical and morphologic features transitional between the two, known as gray zone lymphomas (GZL). However, this diagnostic gray zone is not just of theoretical interest: it presents a practical problem, as the treatment approaches for CHL traditionally differ from those for aggressive B-cell lymphomas. This article reviews the treatment approach for mediastinal lymphomas, including CHL of the nodular sclerosis subtype (CHL-NS), PMBL, and mediastinal GZL. Though several trials have evaluated different regimens with or without radiation in PMBL and CHL-NS, there is a lack of prospective experience in treating GZL because of the rarity of these tumors. Historical data indicate that they have done poorly with traditional approaches developed for the treatment of either CHL or diffuse large B-cell lymphoma.