• In DLBCL, the karyotype with trisomy 18 is usually hyperdiploid with 47-52 chromosomes and with multiple chromosome rearrangements. Trisomy 3 accompanies trisomy 18 in about 30% of cases, and trisomies 7, 12, and 21 in about 10% each. About 10% have a t(14;18) or +der(18)(t(14;18), about 5% have a t(8;14), and another 10% have another 14q32 rearrangement. About 20% have a 6q rearrangement or an i(6)(p10) that results in loss of 6q, and about 20% have an extra X chromosome, many of which are structurally abnormal.

• In FL, the general cytogenetic pattern of cases with trisomy 18 is similar to that of DLBCL. The principle difference is that about 75% of cases exhibit a t(14;18) or an add(14)(q32), and association of trisomy 18 and a t(8;14) is very uncommon.

• Trisomy 18 is a recurrent finding in MZBCL, seen in 39% of cases in one study. About a third of marginal zone lymphomas with trisomy 3 also exhibit trisomy 18.

• About 10% of peripheral T-cell lymphomas exhibit trisomy 18, and then usually as part of a fairly complex karyotype.

Trisomy 18 is observed in 15-33% of lymphomas, including diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), and marginal zone B-cell lymphoma (MZBCL). Trisomy 18 may be less frequent in other NHL sub-types.

Trisomy 18 is strongly associated with a t(14;18) or at least a 14q32 abnormality, and may represent a variant of the +der(18)t(14;18), which duplicates the segment 18pter-18q21. Trisomy 18 is rarely observed as the primary cytogenetic change in NHL.