Surgical excision and cryotherapy
Surgical excision alone has been associated with a higher rate of recurrence compared to excision with adjunctive cryotherapy. Surgical treatment includes complete local excision of the lesion, with at least 3–4 mm margins. Three distinct portions of a typical CIN lesion must be addressed surgically: corneal, limbal, and conjunctival. Occasionally the conjunctival component also
has a deeper extension that must be approached in a specific surgical manner.
the corneal component, the physician can apply absolute alcohol to the affected cornea for 30–40 seconds, followed by copious irrigation with balanced salt solution, in order to devitalize the affected epithelium, killing tumor cells and facilitating epithelial debridement. A No. 64 or No. 69 Beaver blade can be used to scrape the affected cornea to Bowman’s membrane, taking care not to violate the membrane, as this forms a natural barrier to deeper tumor invasion and may lead to more scarring. Scraping is carried out from approximately 1–2 mm into normal cornea, scraping toward the limbus. As the total extent of corneal involvement is sometimes difficult to visualize under the operating microscope, dilating the pupil helps to better visualize the central corneal portion in “retro-illumination.” The use of intraoperative rose bengal staining aids in mapping the entire corneal and conjunctival components of the lesion.
The limbal component is excised with 3–4 mm circumferential margins. If the extent of the CIN is so large that these margins would compromise the amount of residual limbal stem cells, smaller margins can be taken. At least a few clock hours of normal limbal stem cells must remain in order to re-epithelialize
the cornea. The involved limbus can be scraped with a No. 64 or No. 69 Beaver blade, followed by cryotherapy in a double freeze-slow-thaw technique. The slow thaw is thought to cause rupture of cell membranes leading to cell death and potentially killing microscopic disease.
The conjunctival portion is excised with 3–4 mm margins. Care must be taken when dissecting in the area of the rectus muscles. Wet-field cautery is used for hemostasis. The tissue specimen to be sent to pathology for evaluation should be oriented on a piece of filter paper and allowed to dry in place for 30–60 seconds, and the paper should be labeled in pencil prior to placement in formalin. Adjunctive cryotherapy, in a double freeze-slow-thaw technique, is regularly applied to the affected limbus and conjunctival margins in an attempt to eliminate microscopic tumor burden. Cautery may also be helpful in this regard. One need not routinely treat the scleral bed underlying freely mobile conjunctival tumors. If only minimal fixation is noted, cryotherapy to the involved scleral bed is appropriate. If, however, possible deeper involvement is evident or the tumor is fixated to the episclera or sclera, a more aggressive surgical approach is indicated. The degree of surgical aggressiveness is a matter of clinical judgment.
The physician may wish to wait for pathologic confirmation of invasion prior to empiric scleral resection. With obvious tumor involvement, a thin lamellar scleral dissection is performed by outlining the affected sclera with a No. 64 or No. 69 Beaver blade, taking 1–2 mm margins, and using a crescent blade to dissect
off a thin lamellar flap. The No. 64 or No. 69 Beaver blade is passed over the entire area, from cornea, across limbus to sclera, to debride any residual tumor cells and ensure a smooth surface. In cases of severe scleral bed involvement, cryotherapy to the affected area may follow the lamellar dissection.
If extensive tissue is removed, an amniotic membrane, scleral, or corneal graft can be sutured into place over the bare sclera and cornea. In smaller
lesions, the conjunctival margins can be left to heal by secondary intention. 9-0 Vicryl sutures can also be placed to close small-to-moderate conjunctival defects.
If the patient develops limbal stem cell deficiency and problems with epithelialization, a limbal stem cell transplant can be performed once tumor resolution is complete.
Radiation and chemotherapy
Recurrence rates after incomplete surgical resection (positive margins on pathologic evaluation) can reach up to 70% but are usually around 50%. With complete resection (negative margins) the rate of recurrence drops to approximately 5%–10%, although Tabin et al report a rate as high as 30%. This report included varied surgical approaches, from excision alone, to excision with adjunctive radiation or cryotherapy. The time to recurrence after the first excision ranged from 33 days to 11.5 years. The average was 3.8 years for completely excised tumors and 2.5 years for partially excised tumors (positive margins on pathology). Risk factors for recurrence include positive margins and possibly cell type (mucoepidermoid and spindle cell) on pathologic evaluation.
In cases of recurrent tumor or large, annular, limbal lesions, extensive surgical manipulation may lead to compromise of the ocular surface. Specifically, removal of too much tissue may lead to limbal stem cell deficiency
and cicatricial changes. Therefore other treatment options have been used. These include radiation (XRT), mitomycin-C (MMC), 5-fluorouracil (5-FU) and interferon (IFNα2b). Table 1 describes the formulation of these chemotherapeutic agents. Radiation is complicated by retinopathy, corneal epitheliopathy, and cataract formation, and has fallen out of favor. To spare limbal cells, patients who have already had one or more excisions with confirmed pathologic diagnosis are ideal candidates for medical/chemotherapeutic treatment as are patients with primary annular lesions requiring greater than 180°–270° of excision.
MMC is an alkylating agent that blocks cell growth at any stage of the cell cycle by cross-linking DNA and inhibiting DNA synthesis. It has been used successfully as topical treatment of CIN/SCCA. The concentrations range from 0.02% (200 g/ml) to 0.04% (400g/ml), four times daily. Published success rates have ranged from 76% to 100%. Most studies have concluded that use for longer than 14 days can lead to severe irritative symptoms (pain, photophobia, blepharospasm). The use of topical MMC can also be complicated by hyperemia, allergy, corneal epithelialopathy, and possibly scleral melting. For that reason, most clinicians treat in cycles of up to 14 days, with a 1–2-week rest period between cycles. As many as four cycles can be necessary to affect a cure. Some ocular surface side effects can be successfully treated with the administration of topical steroid drops three to four times per day in the rest period while MMC is discontinued. The use of punctal plugs during treatment with MMC prevents punctal stenosis and absorption into the nasal mucosa. MMC requires refrigeration and must be discarded after 2 weeks. If tolerated by the patient, the 14-day treatment regimen maximizes the shelf life and cost of MMC.
5-FU is a pyrimidine analogue that inhibits DNA synthesis in the S-phase of the cell cycle. Different treatment regimens have been described. Midena et al used a 1% 5-FU solution given four times a day for 4 weeks to effectively treat SCCA. Seven of eight patients demonstrated complete regression, while one patient was cured after a second 4-week retreatment. Alternatively, as described by Yeatts at al, 1% 5-FU four times a day has been used for 2–4 day cycles, with 30–45 days between cycles, for a total of two to five cycles. Using this regimen, four out of seven patients were cured, two of the remaining patients improved with re-treatment, while one patient required MMC treatment to achieve resolution. Like MMC, 5-FU may lead to ocular surface irritation, corneal defects, and skin discomfort, but the 2–4 days-per-month dosing is well tolerated. 5-FU is less costly and does not need refrigeration.
Interferon alfa-2b (IFNα2b) is a protein with antiproliferative and antiviral properties that cells secrete in response to several different stimuli, including viral infection. The exact mechanism of action, however, is not yet known. The FDA has approved the use of IFNα2b to treat diseases such as hepatitis B and C, Kaposi’s sarcoma, malignant melanoma, condyloma acuminata, and hairy cell leukemia. It has also been used successfully in the treatment of cervical intraepithelial neoplasia and squamous lesions of the skin (which, like SCCA, have been associated with HPV). Intralesional and/or subconjunctival injections of IFNα2b, with concomitant topical use, have achieved ocular tumor resolution (Figure 6). One treatment regimen includes the injection of 0.5 ml of a 3 million IU/0.5ml solution of recombinant IFNα2b (INTRON A, Schering Plough, Kenilworth, New Jersey) combined with topical IFNα2b (1 million IU/ml drops) four times daily. Tumor resolution seems to require dosing correlated with the size of the lesion, and injections may need to be repeated every week (up to three times a week) until clinical resolution is observed. The topical IFNα2b may be tapered slowly (decreasing one drop a day over 1-month increments).
Successful treatment of CIN/SCCA with topical IFNα2b (1 million IU/ml four times a day) alone has been described by several investigators. The physician may find that topical administration of interferon (IFN) is effective but produces a slower resolution compared with injections of IFN. Side effects of injected IFNα2b include fever and myalgias (flu-like symptoms), which tend to improve with acetaminophen use. Topical IFNα2b is well tolerated with no reported systemic side effects.
The initial protocol for patients who are not surgical candidates, who develop recurrence, or have annular lesions, includes the use of a topical chemotherapeutic agent. Topical IFN is gentle and easily tolerated by the patient. It is, however, slower than MMC. Injection of IFN (3 million IU/ml, 0.5 cc) may be used with patients where compliance is an issue, or in the case of thicker, larger lesions. The response rate to resolution is quicker with injections, but patients tend to prefer drops. The tumor response with injection appears to be dose-dependent. Patients who prefer not to have periocular injections may be treated topically. Patients need to be advised that topical treatment with IFN may
take 3 months or more. Topical IFNα2b is given four times a day. If the tumor responds, this treatment may be continued and tapered slowly as described above.