Summary

Trisomy 5 as the sole cytogenetic aberration in acute lymphoblastic leukaemia (ALL) is exceedingly rare. As such, its prognostic and therapeutic relevance remains unknown. We report a case of an 18-year-old young man who was diagnosed with B cell ALL with trisomy 5 as the sole chromosomal abnormality. He was treated with chemotherapy and went into complete remission. On the 14th month of treatment, he relapsed with central nervous system involvement characterised by leukaemic infiltration of the optic nerve and facial palsy. He subsequently underwent reinduction chemotherapy with aggressive intrathecal chemotherapy followed by posterior globe and whole brain radiation therapy. He is currently on his 26th month of treatment, in second remission, with complete resolution of leukaemic infiltrative optic neuropathy and facial paralysis. As more cases of this nature are reported, we will be able to determine the relevance of this distinct cytogenetic entity.