Purpose

To report two cases of ocular adnexal collision tumors, characterized by two histologically distinct tumors coexisting at a single anatomical site, and highlight their diagnostic and therapeutic challenges.

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Methods

Retrospective review of clinical and histopathologic data from two patients presenting to a tertiary eye center.

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Results

Case 1: An 80-year-old male with a history of facial non-melanoma skin cancers presented for re-evaluation of a right orbital mass previously diagnosed via biopsy as extranodal marginal zone lymphoma (EMZL). Prior MRI orbits showed an infiltrative mass involving the orbital apex and cavernous sinus. Despite radiation and rituximab, the patient developed vision loss, complete ophthalmoplegia, and V1 hypoesthesia, atypical for EMZL. Repeat MRI showed intracranial and perineural extension. PET-CT showed new intense FDG-avidity in the left upper lung lobe. Subsequent deeper biopsy revealed a collision tumor composed of EMZL and infiltrative basal cell carcinoma (BCC). The patient transitioned to hospice and passed shortly thereafter.

Case 2: A 42-year-old HIV-negative male with a history of Mpox and hepatitis C, previously treated with doxorubicin for conjunctival Kaposi sarcoma (KS) of the left eye, presented with recurrent conjunctival lesions. Biopsy revealed a collision tumor composed of KS and EMZL. Staging PET showed no systemic uptake. Following radiotherapy, initial regression was achieved. However, one year later, EMZL recurred bilaterally without evidence of recurrent KS.

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Conclusion

Collision tumors of the ocular adnexa may present as treatment-refractory disease. These cases highlight the importance of rebiopsy when clinical trajectory deviates from expected behavior or treatment response. Recognizing the coexistence of multiple tumor types is critical for treatment planning and prognosis, as treating one component of a collision tumor, such as rituximab for EMZL, may inadvertently accelerate progression of a coexisting tumor. To our knowledge, these represent the first reported ocular BCC–EMZL and KS–EMZL collision tumors.

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Additional Authors

First name	Last name	Base Hospital / Institution
David	Zhao	Massachusetts Eye and Ear, Harvard Medical School
Hursuong	Vongsachang	Massachusetts Eye and Ear, Harvard Medical School
Carolina A.	Chiou	Massachusetts Eye and Ear, Harvard Medical School
Lisa Y.	Lin	Massachusetts Eye and Ear, Harvard Medical School
Anna M.	Stagner	Massachusetts Eye and Ear, Harvard Medical School
Michael K.	Yoon	Massachusetts Eye and Ear, Harvard Medical School

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