Purpose

Signet ring cell/histiocytoid carcinoma (SRCHC) is an exceptionally rare epithelial malignancy, predominantly involving the eyelid, and less commonly, extraocular sites such as the axilla. Diagnosis is often challenging owing to its histological resemblance to lobular breast carcinoma and diffuse gastric carcinoma, necessitating systemic investigation to exclude a primary or metastatic source.

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Methods

We report the case of an 80-year-old woman in whom an incidental conjunctival lesion, clinically resembling a benign squamous papilloma, was identified during routine punctoplasty. The lesion was biopsied intraoperatively, followed by comprehensive systemic evaluation, including PET-CT, and multidisciplinary team review.

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Results

Histopathology confirmed features consistent with SRCHC. Initial systemic evaluation demonstrated avid retroperitoneal lymphadenopathy suspicious for metastatic disease, without identification of a primary malignancy. Following multidisciplinary team review, including breast and gastroenterology input, no primary source was identified. In the absence of orbital involvement or further disease on PET-CT, the relationship between the conjunctival lesion and retroperitoneal lymphadenopathy remains uncertain, raising the possibility of separate disease processes. The case has been classified as a cancer of unknown primary, and further investigations are ongoing.

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Conclusion

This case represents a novel conjunctival presentation of SRCHC and highlights the diagnostic complexity of distinguishing primary from metastatic disease in rare periocular malignancies. It underscores the importance of histopathological and multidisciplinary input, particularly in cases of diagnostic uncertainty. To our knowledge, conjunctival involvement in SRCHC has not previously been described.

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Additional Authors

First name	Last name	Base Hospital / Institution
Naomi Aloka	Aloka	Luton and Dunstable University Hospital
Caroline	Graham	Luton and Dunstable University Hospital
Engin	Akyol	Luton and Dunstable University Hospital
Susan	Sarangapani	Luton and Dunstable University Hospital

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