Occult collision tumor of the gastroesophageal junction comprising adenocarcinomas with distinct molecular profiles.

Collision tumors, characterized by the coexistence of two unique neoplasms in close approximation, are rare and pose diagnostic challenges. This is particularly true when the unique neoplasms are of the same histologic type. Here we report such a case where comprehensive tumor profiling by next generation sequencing (NGS) as well as immunohistochemistry revealed two independent adenocarcinomas comprising what was initially diagnosed as a single adenocarcinoma of the gastroesophageal (GEJ) junction. Biopsy of the esophageal portion of the GEJ mass showed a mismatch repair deficient tumor with loss of immunoreactivity for MLH1 and PMS2, while the biopsy taken from the gastric portion of the mass revealed a separate tumor with a discordant, non-overlapping, set of molecular alterations, including an EML4::ALK fusion, as well as intact MMR. This case illustrates one way in which NGS can reveal diagnoses such as collision tumor that are wholly unexpected based on clinical and histological grounds. Such diagnoses can have important implications for patient care, particularly in cases where there is discordance for targetable molecular alterations.
Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Shridar Ganesan reports a relationship with Merck that includes: employment and equity or stocks. Shridar Ganesan reports a relationship with Ibris Inc that includes: equity or stocks. Shridar Ganesan reports a relationship with Inspirata Inc that includes: consulting or advisory and equity or stocks. Shridar Ganesan reports a relationship with Silagene that includes: consulting or advisory and equity or stocks. Shridar Ganesan reports a relationship with Novartis that includes: consulting or advisory. Shridar Ganesan reports a relationship with Roche that includes: consulting or advisory. Shridar Ganesan reports a relationship with Foghorn Therapeutics that includes: consulting or advisory. Shridar Ganesan reports a relationship with Foundation Medicine Inc that includes: consulting or advisory. Shridar Ganesan reports a relationship with Merck Sharp & Dohme that includes: consulting or advisory. Shridar Ganesan reports a relationship with EQRx that includes: consulting or advisory. Shridar Ganesan reports a relationship with EMD Serono Inc that includes: consulting or advisory. Shridar Ganesan reports a relationship with KayoThera that includes: consulting or advisory. Shridar Ganesan reports a relationship with Ipsen that includes: consulting or advisory. Shridar Ganesan reports a relationship with M2Gen that includes: funding grants. Shridar Ganesan reports a relationship with Gandeeva that includes: funding grants. Gregory M. Riedlinger reports a relationship with AstraZeneca that includes: consulting or advisory. Gregory M. Riedlinger reports a relationship with Pfizer that includes: consulting or advisory. Shridar Ganesan has patent licensed to Ibris, Inc. Shridar Ganesan has patent licensed to Inspirata, Inc. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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