Tumor Size

Uveal melanoma most often assumes a nodular or dome-shaped configuration, but occasionally tumors can be flat or diffuse and involve extensive areas of the uvea with little elevation.

Tumor size classifications according to boundary lines are as follows:

1. SMALL: Range from 1 mm to 3 mm in apical height and have a basal diameter of at least 5 mm.[1]
2. MEDIUM: Range from 2 mm to 3 mm up to 10 mm in apical height and have a basal diameter of less than 16 mm.[2]
3. LARGE: Greater than 10 mm in apical height or have a basal diameter of at least 16 mm.[3]
4. DIFFUSE: Horizontal, flat growth pattern, with the thickness of the tumor measuring approximately 20% or less than the greatest basal dimension; this uncommon variant of uveal melanoma seems to have a poorer prognosis.[4]

In clinical practice, the tumor base may be estimated in average optic disc diameters (1 dd = 1.5 mm). The average elevation may be estimated in diopters (3 diopters = 1 mm). Other techniques, such as ultrasonography, should be used to provide more accurate measurements.

An important function of ophthalmic ultrasonography is the detection of extrascleral extension.[5,6] Extrascleral extension measuring 2 mm or more in thickness can invariably be demonstrated provided it is located behind the equator where the intraocular tumor, sclera, and adjacent orbital fat are readily imaged.[7] Orbital extraocular extension of choroidal melanoma may be found in eyes with medium and large tumors, but it is very rare in eyes with small melanomas.

Metastatic Disease

Because the uveal tract is a vascular structure without lymphatic channels, tumor spread occurs principally by local extension and by dissemination through the blood stream. If regional preauricular, submandibular, or cervical lymph node involvement is seen, subconjunctival extension of the primary tumor has occurred.[8]

Systemic metastases are generally hematogenous in origin, and the first site identified is usually the liver.[9] Lung, bone, and subcutaneous sites are also common.[9] In the Collaborative Ocular Melanoma Study trials, the liver was the only site of detectable metastasis in 46% of patients with metastases reported during follow-up or at the time of death; 43% had metastases diagnosed in the liver and other sites.[9] In patients with a history of ocular melanoma who present with hepatic metastases of unknown origin, metastatic melanoma should be considered in the differential diagnosis.

It is particularly unusual for choroidal melanomas of any size to invade the optic nerve or its meninges.[10] Metastasis of choroidal melanoma to the contralateral choroid is also rare.[9,11]

Other Classification and Staging

An American Joint Committee on Cancer staging system has been developed for melanoma of the uveal tract,[12] and its widespread utilization has been advocated.[13]

References:

1. Factors predictive of growth and treatment of small choroidal melanoma: COMS Report No. 5. The Collaborative Ocular Melanoma Study Group. Arch Ophthalmol 115 (12): 1537-44, 1997.
2. Diener-West M, Earle JD, Fine SL, et al.: The COMS randomized trial of iodine 125 brachytherapy for choroidal melanoma, II: characteristics of patients enrolled and not enrolled. COMS Report No. 17. Arch Ophthalmol 119 (7): 951-65, 2001.
3. The Collaborative Ocular Melanoma Study (COMS) randomized trial of pre-enucleation radiation of large choroidal melanoma I: characteristics of patients enrolled and not enrolled. COMS report no. 9. Am J Ophthalmol 125 (6): 767-78, 1998.
4. Shields CL, Shields JA, De Potter P, et al.: Diffuse choroidal melanoma. Clinical features predictive of metastasis. Arch Ophthalmol 114 (8): 956-63, 1996.
5. Scott IU, Murray TG, Hughes JR: Evaluation of imaging techniques for detection of extraocular extension of choroidal melanoma. Arch Ophthalmol 116 (7): 897-9, 1998.
6. Romero JM, Finger PT, Iezzi R, et al.: Three-dimensional ultrasonography of choroidal melanoma: extrascleral extension. Am J Ophthalmol 126 (6): 842-4, 1998.
7. Echography (ultrasound) procedures for the Collaborative Ocular Melanoma Study (COMS), Report no. 12, Part I. J Ophthalmic Nurs Technol 18 (4): 143-9, 1999 Jul-Aug.
8. Dithmar S, Diaz CE, Grossniklaus HE: Intraocular melanoma spread to regional lymph nodes: report of two cases. Retina 20 (1): 76-9, 2000.
9. Diener-West M, Reynolds SM, Agugliaro DJ, et al.: Development of metastatic disease after enrollment in the COMS trials for treatment of choroidal melanoma: Collaborative Ocular Melanoma Study Group Report No. 26. Arch Ophthalmol 123 (12): 1639-43, 2005.
10. Shields CL, Santos MC, Shields JA, et al.: Extraocular extension of unrecognized choroidal melanoma simulating a primary optic nerve tumor: report of two cases. Ophthalmology 106 (7): 1349-52, 1999.
11. Singh AD, Shields JA, Shields CL, et al.: Choroidal melanoma metastatic to the contralateral choroid. Am J Ophthalmol 132 (6): 941-3, 2001.
12. Malignant melanoma of the uvea. In: American Joint Committee on Cancer.: AJCC Cancer Staging Manual. 6th ed. New York, NY: Springer, 2002, pp 365-70.
13. Finger PT: Do you speak ocular tumor? Ophthalmology 110 (1): 13-4, 2003.