[1][2][3] While it had previously been considered a subtype of diffuse large B-cell lymphoma;,[4] the World Health Organization no longer classifies it as such, based on distinct clinicopathologic and molecular features.

[6] Molecular analysis shows that PMLBCL is distinct from other types of diffuse large B-cell lymphomas (DLBCL).

Despite 80% PMLBCL being stage I or II, the presenting anterior mediastinal mass is often over 10 cm and is locally invasive of lung, chest wall, pleura, and pericardium.

[6] At initial presentation, PMLBCL is usually confined to mediastinum, but its bulk, rather than additional adenopathy, can sometimes be palpated at the low neck.

[10] Tumors that are even more closely related to NSHL than typical for PMBCL are called gray zone lymphoma.