Imaging Manifestations of Pseudoprogression in Metastatic Melanoma Nodes Injected with Talimogene Laherparepvec: Initial Experience

Abstract

Talimogene laherparepvec is an oncolytic virus recently approved for targeted treatment of advanced melanoma. Because of an inflammatory reaction, treated lesions may increase in size and develop infiltrative margins that can be construed as disease progression or extracapsular spread. In this report, we describe our initial experience imaging the response of metastatic nodes injected with talimogene laherparepvec. Six of 12 nodes (50%) showed growth from baseline followed by decreased size, 5 of 12 nodes (42%) showed a downward size trend, and 1 node showed continued increase in size. Seven of 9 nodes (78%) developed infiltrative margins at a median of 79 days, and 6 of 9 (67%) nodes became necrotic at a median of 76 days after injection, all showing decreased size at final follow-up. An increase in the size of nodes injected with talimogene laherparepvec does not necessarily indicate progression. Infiltrative margins are also frequently seen and may be confused with extracapsular disease.

Fig 1.

Line graph showing change in size over time relative to baseline CT. A, Fifty percent of nodes showed initial growth followed by decreased size. One node (marked with an asterisk at last time point) demonstrated a continued increase in size, but could not be followed after 184 days. B, Forty-two percent of nodes showed a downward trend in size. The final size was smaller than baseline in all nodes except for the one indicated in A.

Fig 2.

A, Coronal contrast-enhanced CT shows a round, well-circumscribed necrotic lesion (black arrow) at the inferior aspect of the right parotid gland. B, The lesion has increased in size and developed infiltrative margins (white arrow) 72 days after injection. Follow-up at 111 days (C) and 184 days (D) after injection demonstrates further growth and marked increase in central necrosis. E, The lesion shows decreased size after 337 days.

Fig 3.

A, Axial contrast-enhanced CT shows a small nodule in the deep right breast/axillary region (white arrow). The lesion shows slight central hypoattenuation and increased size at 34 days after injection (white arrow, B) with the development of frank central necrosis after 72 days (black arrow, C). There is a mild further increase in size at 104 days (D), followed by decreased size at 125 days (E) and near complete resolution at 174 days (F).