Chromosome studies in a 7-week-old female infant with an intraabdomina
l malignant fibrosarcoma showed a hyperdiploid karyotype of 50,XX, +de
r(6)del(6)(p23)add(6)(q11), +8, +10, +11,add(12)(p13). Trisomy 11 appe
ars to be a nonrandom primary cytogenetic abnormality in the congenita
l or infantile form of this mesenchymal tumor and is also a nonrandom
gain in congenital mesoblastic nephroma. A possible developmental link
between these two mesenchymal tumors, mediated by a gene or genes on
chromosome 11 is postulated.