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Table 3. Metastasis (M)a

M0No metastasis.
M1Systemic metastasis.
M1aSingle lesion to sites other than CNS.
M1bMultiple lesions to sites other than CNS.
M1cPrechiasmatic CNS lesion(s).
M1dPostchiasmatic CNS lesion(s).
M1eLeptomeningeal and/or CSF involvement.

CNS = central nervous system; CSF = cerebrospinal fluid.
aReprinted with permission from AJCC: Retinoblastoma. In: Edge SB, Byrd DR, Compton CC, et al., eds.: AJCC Cancer Staging Manual. 7th ed. New York, NY: Springer, 2010, pp 562–63.