Ocular Surface Squamous Neoplasia (OSSN)

Key Points at a Glance

1. What is Ocular Surface Squamous Neoplasia (OSSN)?

The term was proposed by Lee et al. in 1995 and encompasses non-complex squamous epithelial tumors arising from the cornea, conjunctiva, and limbus ¹⁾. It is the most common non-pigmented tumor of the ocular surface; in a single-center study, OSSN accounted for 23% (179 cases) of 771 non-melanocytic conjunctival tumors ¹⁾.

OSSN includes the following lesions:

Conjunctival intraepithelial neoplasia (CIN): Non-invasive intraepithelial lesion. Classified as CIN I (mild), CIN II (moderate), and CIN III (severe/carcinoma in situ) based on the degree of dysplasia ¹⁾
Squamous cell carcinoma (SCC): The most advanced form of OSSN. Dysplastic cells penetrate the basement membrane and invade the stroma ¹⁾
Mucoepidermoid carcinoma: A rare and aggressive subtype of SCC. It occurs more often in elderly individuals and contains yellow cystic components ¹⁾

Epidemiology

The incidence varies greatly by geographic region. In high-latitude areas, it is 0.02 per 100,000, while in low-latitude regions near the equator, it reaches 3.5 per 100,000¹⁾. The global age-standardized incidence rate is 0.26 per 100,000 per year and is increasing¹⁾. Africa has the highest rate (3.4 per 100,000 per year), with high frequencies of HIV and HPV infection contributing¹⁾.

In the Western Hemisphere, it commonly occurs in white men over 60 years old, but in parts of Africa and Asia, it also affects younger individuals with HIV infection and follows a more aggressive course¹⁾.

Staging (AJCC 8th Edition TNM Classification)

The AJCC 8th edition classifies OSSN based on primary tumor (T), regional lymph nodes (N), and distant metastasis (M)¹⁾.

Classification	Definition
Tis	Carcinoma in situ (confined to epithelium)
T1	Confined to conjunctiva, no invasion of adjacent structures
T2	Invasion of adjacent ocular structures (cornea, fornix, caruncle, sclera, globe)
T3	Invasion of orbit, paranasal sinuses, or eyelid
T4	Invasion of central nervous system or distant sites

Untreated SCC can lead to orbital invasion (approximately 10%), regional lymph node metastasis, and rarely distant metastasis, with reported mortality rates of 8–24% ¹⁾.

2. Main Symptoms and Clinical Findings

Al Bayyat G, Arreaza-Kaufman D, Venkateswaran N, Galor A, et al. Update on pharmacotherapy for ocular surface squamous neoplasia. Eye Vis (Lond). 2019 Aug 12;6:24. Figure 2. PMCID: PMC6689886. License: CC BY.

Anterior segment photograph showing a gelatinous, white elevated lesion extending from the limbus to the corneal surface. The conjunctival and corneal lesion with irregular surface and borders demonstrates the appearance of ocular surface squamous neoplasia.

Subjective Symptoms

OSSN lesions are often asymptomatic and discovered incidentally. When symptoms are present, they mainly include redness, foreign body sensation, and ocular irritation ²⁾. Pain may also occur. Visual loss is seen when the tumor involves the cornea or in cases of intraocular invasion.

Clinical Findings

A unilateral vascularized mass is most common, typically occurring near the limbus in the interpalpebral fissure (nasal or temporal side) ¹⁾. It frequently involves the cornea and bulbar conjunctiva, while palpebral conjunctival involvement is rare ¹⁾. In Caucasians, the lesion appears yellow-pink; in pigmented races, it may be pigmented ¹⁾³⁾.

Gelatinous

Translucent elevated mass: The most common form. Conjunctival vessels show a hairpin-like course.

Feeder vessels: Abnormally dilated and tortuous feeding arteries suggest malignant growth ¹⁾.

Leukoplakic

White thickened surface: Keratinization of the tumor surface due to hyperkeratosis.

Dry appearance: It presents an opaque white color, in contrast to gelatinous.

Papillomatous

Papillomatous growth: Known as an HPV-associated morphology ⁴⁾.

Nodular surface: May have a wart-like appearance.

Noduloulcerative

Rare but invasive: A morphology strongly suggestive of invasive neoplasm ¹⁾.

Ulceration: Worse prognosis than other forms.

Corneal involvement presents a translucent, grayish ground-glass appearance with fimbriated or pseudopodial extension.

Intraocular invasion is rare but may present as a white mass in the anterior chamber, anterior chamber inflammation, or secondary glaucoma ²⁾.

Q Can OSSN present as a pigmented lesion?

Yes. Especially in HIV-positive individuals of color, CIN has been reported to mimic pigmented lesions ³⁾. Even in the absence of typical OSSN findings, conjunctival pigmented lesions in HIV-positive patients should include OSSN in the differential diagnosis.

3. Causes and Risk Factors

The etiology of OSSN is multifactorial. Major risk factors are listed below ¹⁾.

Ultraviolet exposure: The greatest risk factor. High incidence within 30 degrees latitude of the equator. Also explains the predilection for the interpalpebral fissure.
Age and sex: More common in men over 60 years old. Outdoor occupations also increase risk.
HIV/AIDS: Immunosuppression increases risk by 10–13 times ³⁾. In Africa, HIV infection leads to high incidence even in young women ¹⁾. OSSN may be an initial indicator of undiagnosed HIV ³⁾
HPV infection: Association with HPV types 16 and 18 has been reported, but remains controversial ¹⁾
Others: Smoking, xeroderma pigmentosum, vitamin A deficiency, chemical exposure, ocular surface trauma ¹⁾

Q Why are people with HIV more prone to OSSN?

Because immunosuppression due to HIV infection impairs tumor immune surveillance. In HIV-positive individuals, OSSN risk increases 10–13 times ³⁾, and it can occur at a young age. In Africa, co-infection with HIV and HPV is considered a contributing factor to the increase in the disease ¹⁾.

4. Diagnosis and Examination Methods

Definitive Diagnosis

The definitive diagnosis of OSSN is histological examination by excisional or incisional biopsy (gold standard) ¹⁾. For small tumors less than 4 hours, excisional biopsy is indicated; for large tumors 4 hours or more, incisional biopsy is appropriate.

Auxiliary Diagnostic Methods

High-resolution anterior segment OCT (HR-OCT): Characteristic findings include epithelial thickening, hyperreflectivity, and an abrupt transition from normal to abnormal tissue. It allows noninvasive assessment of tumor extent and is useful for monitoring treatment response ¹⁾⁴⁾
In vivo confocal microscopy (IVCM): Allows noninvasive evaluation of cellular-level details ¹⁾
Impression cytology and exfoliative cytology: Evaluate superficial dysplastic cells but cannot determine depth of invasion ¹⁾

Special Staining

Special stains such as rose bengal, lissamine green, methylene blue, and toluidine blue are used to aid diagnosis ¹⁾. Rose bengal stains apoptotic and metabolically inactive epithelial cells a vivid pink, clarifying the tumor margins ¹⁾.

The main diagnostic modalities are summarized below.

Test	Features
Biopsy (histopathology)	Gold standard. Can assess depth of invasion.
HR-OCT	Noninvasive. Characterized by epithelial thickening and hyperreflectivity.
IVCM	Cellular-level assessment. Technically demanding.
Impression cytology	Noninvasive but only evaluates surface tissue.

Differential Diagnosis

OSSN must be differentiated particularly from pterygium and pinguecula ¹⁾. They may coexist, making diagnosis challenging. Other differentials include corneal pannus, actinic keratosis, pyogenic granuloma, conjunctival nevus, and malignant melanoma.

Q How to distinguish OSSN from pterygium?

When clinical findings alone make differentiation difficult, epithelial thickening and hyperreflectivity on HR-OCT, as well as special staining with rose bengal or methylene blue, can provide clues for differential diagnosis ¹⁾. Biopsy is required for definitive diagnosis.

5. Standard Treatment

Treatment of OSSN is individualized based on tumor size, depth of invasion, and patient factors ¹⁾. Surgical excision and topical chemotherapy have been reported to have equivalent efficacy ¹⁾.

Surgical Treatment

No-touch technique plus cryotherapy is the gold standard ¹⁾.

The tumor is not directly grasped; a 3–4 mm safety margin of clinically normal tissue is ensured during excision.
For corneal lesions, absolute alcohol is applied to detach the epithelium from the basement membrane, preserving the underlying Bowman’s layer.
Double or triple rapid freeze-thaw cryotherapy is applied to the excision margins, limbus, and exposed scleral bed.
The excision site may be reconstructed with amniotic membrane transplantation.

If the excision margins are positive, postoperative adjuvant chemotherapy is recommended ¹⁾²⁾. Without cryotherapy or postoperative chemotherapy, the risk of intraocular invasion increases ²⁾.

Pike et al. (2023) reported a case of OSSN in which, without cryotherapy or chemotherapy after excision, intraocular seeding (anterior chamber mass formation) occurred through a full-thickness limbal defect, leading to enucleation ²⁾. This highlights the importance of the no-touch technique, cryotherapy, and postoperative chemotherapy.

Medical Therapy

Topical chemotherapy is used both as monotherapy and as postoperative adjuvant therapy ¹⁾.

Mitomycin C

Mitomycin C: 0.02–0.04% eye drops. It kills tumor cells by crosslinking DNA.

Efficacy rate: 80–100%. Time to resolution tends to be shorter than with IFN¹⁾.

Side effects: Ocular pain, limbal stem cell deficiency, risk of punctal stenosis.

5-FU

5-Fluorouracil: A pyrimidine analog that inhibits DNA and RNA synthesis in the S phase¹⁾.

Efficacy rate: High. Recurrence rate up to 20%. Less expensive than mitomycin C and IFN.

Administration: Used in cycles of 1% eye drops for 1 week followed by 3 weeks off.

IFNα-2b

Interferon α-2b: Has antiproliferative, antiviral, and immunomodulatory effects¹⁾.

Efficacy rate: 80–100%. Administered via subconjunctival injection (1 million IU/mL) or eye drops.

Features: Few side effects but expensive and requires refrigeration.

Other drug therapies include anti-VEGF agents (bevacizumab, ranibizumab), which show promising results for conjunctival lesions but unclear effects on corneal lesions; large-scale trials are needed¹⁾. Cidofovir may be used in HPV-related patients¹⁾.

Treatment strategy based on AJCC TNM classification

The treatment approach based on the AJCC 8th edition is shown below¹⁾.

T1 (≤5 mm, confined to conjunctiva): Excisional biopsy + cryotherapy, or topical chemotherapy (MMC, 5-FU, IFNα-2b)
T2 (>5 mm or invasion of adjacent structures): Wide excision + adjuvant chemotherapy. Preoperative chemotherapy may be used to reduce tumor size.
T3-T4 (orbital or distant invasion): Combination with radiotherapy; for highly invasive cases, enucleation or orbital exenteration.

Risk factors for recurrence

The following factors are associated with recurrence¹⁾.

Large tumor size
Advanced age
Positive resection margins
HIV infection (recurrence rate 3–43%)³⁾
High grade
Presence of feeder vessels
High proliferative index

Q Which is more effective for OSSN: surgery or drug therapy?

Chemotherapy alone (MMC, 5-FU, IFNα-2b) has been reported to be as effective as surgery¹⁾. The choice depends on tumor size, depth of invasion, patient’s general condition, and adherence. For lesions larger than 4 hours, multiple lesions, or recurrent cases, topical chemotherapy may be advantageous.

6. Pathophysiology and detailed pathogenesis

Origin and Histology

OSSN is thought to arise from limbal stem cells ¹⁾. Most primary conjunctival malignancies occur near the limbus within the interpalpebral fissure, where stem cell division is active ¹⁾.

Histologically, in invasive SCC, malignant squamous epithelial cells penetrate the basement membrane and proliferate in the stroma ¹⁾. CIN I to III are classified by the extent of dysplasia within the epithelium. Full-thickness epithelial dysplasia (CIN III) is synonymous with carcinoma in situ ¹⁾.

Molecular Mechanisms of Carcinogenesis

Ultraviolet radiation and p53 mutation: UV-B irradiation induces mutations in the p53 gene, leading to disruption of apoptosis control and tumor development.
HPV and E6/E7 proteins: The E6 protein of high-risk HPV (types 16 and 18) degrades p53, and the E7 protein inactivates the Rb protein, resulting in loss of cell cycle control.
Immunosuppression: Impaired tumor immune surveillance due to HIV infection promotes OSSN development ¹⁾.

Mechanisms of Intraocular Invasion

Intraocular invasion is rare but occurs via the following routes ²⁾:

Direct scleral invasion
Tumor cell seeding from surgical wounds (excision sites)
Spread through anterior ciliary vascular channels

In the case by Pike et al. (2023), a full-thickness limbal defect formed after excisional biopsy, through which tumor cells seeded into the anterior chamber and spread to the posterior corneal surface, angle, iris, ciliary body, and lens ²⁾. Pathologically, the findings resembled a malignant form of epithelial downgrowth.

In mucoepidermoid carcinoma, mucin staining reveals dysplastic squamous epithelial cells and malignant goblet cells. When the mucin component is predominant, clinical aggressiveness is considered relatively low.

7. Latest Research and Future Prospects (Investigational Reports)

Radiation Therapy

Radiation therapy is being considered as a treatment option for OSSN and SCC ¹⁾.

External beam radiation therapy (EBRT): Proton beams or electron beams are used, which are excellent at sparing adjacent healthy tissue. There are reports of avoiding enucleation in large tumors with intraocular invasion ¹⁾
Brachytherapy: Uses radioactive plaques with isotopes such as strontium-90, iodine-125, and ruthenium-106. There are reports of achieving tumor control even in cases with positive resection margins ¹⁾

Photodynamic Therapy (PDT)

This is a treatment combining verteporfin and laser ¹⁾. In a pilot study, tumor disappearance was achieved in 100% of conjunctival SCC cases, with no recurrence during the observation period ¹⁾. However, high cost, limited facilities, and the need for specialized training are barriers to widespread adoption.

Treatment with HPV Vaccine

Zein et al. (2024) administered four intramuscular injections of the 9-valent HPV vaccine (Gardasil-9) at 6-week intervals to a patient with recurrent papillary OSSN (HPV-positive, p16-positive) after two resections ⁴⁾. Dramatic tumor shrinkage was observed after the third injection, and HR-OCT confirmed improvement in epithelial thickening and hyperreflectivity. However, a cure was not achieved, and additional topical 5-FU and mitomycin C were administered.

This is the world’s first report of using the HPV vaccine for OSSN treatment ⁴⁾, and research is ongoing as a future treatment option. The therapeutic mechanism is presumed to involve suppression of HPV-specific E6/E7 oncoproteins ⁴⁾.

8. References

Tsatsos M, Delimitrou C, Tsinopoulos I, Ziakas N. Update in the Diagnosis and Management of Ocular Surface Squamous Neoplasia (OSSN). J Clin Med. 2025;14(5):1699.
Pike S, Engelhard SB, Sibug Saber ME, et al. Intraocular Spread of Ocular Surface Squamous Neoplasia Presenting as a Postoperative Anterior Chamber Opacity after Excisional Biopsy. Case Rep Ophthalmol. 2023;14:194-202.
Ta J, Manade V, Kotecha MR, et al. Conjunctival Intraepithelial Neoplasia Mimicking a Pigmentary Lesion in an HIV-Seropositive Indian Male. Cureus. 2024;16(4):e58953.
Zein M, De Arrigunaga S, Amer MM, et al. Therapeutic Response to Treatment of a Papillomatous Ocular Surface Squamous Neoplasia with Intramuscular Human Papillomavirus Vaccine. Cornea. 2024;43(8):1049-1052.

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