Identification and molecular characterisation of a CALM-AF10 fusion in acute megakaryoblastic leukaemia

The t(10;11)(p13;q14-21) is a non-random translocation described in acute lymphoblastic and myeloid leukaemias. It results in the fusion of the gene CALM, which encodes a clathrin assembly protein, on 11q14 to the gene AF10, a putative transcription factor on 10p13. Here we describe for the first time, the occurrence of a CALM-AF10 fusion in a case of acute megakaryoblastic leukaemia. Fluorescence in situ hybridisation and reverse transcriptase polymerase chain reaction were used to confirm the presence of a CALM-AF10 fusion. A novel splice variant of CALM missing nt 1927-2091 was also detected. Though CALM is a cytoplasmic protein, the chimaeric fusion product is able to localise to both the nucleus and cytoplasm. Analysis of the fusion variants suggests, however, that the critical fusion product is likely to be cytoplasmic and contain the interactive leucine zipper of AF10.

Hemihypertrophy and a poorly differentiated embryonal rhabdomyosarcoma of the pelvis

BACKGROUND

Asymmetry of the limbs (conventionally known as hemihypertrophy) is one of the overgrowth syndromes occurring sporadically in the general population at a frequency of approximately 1:86,000. Hemihypertrophy is also reported as part of the Beckwith-Wiedemann syndrome which has as its cardinal features omphalocele, macroglossia and gigantism with hypoglycemia, organomegaly, renal anomalies, hemihypertrophy, and embryonal tumors occurring less frequently. Various neoplasms are also associated with isolated hemihypertrophy. Wilms tumor, adrenocortical carcinoma, and hepatoblastoma are the most frequent. Rhabdomyosarcoma, neuroblastoma, phaeochromocytoma, and undifferentiated sarcoma of the lung are encountered only rarely. Loss of heterozygosity (LOH) of chromosome 11p15.5 is strongly associated with childhood embryonal tumors, particularly Wilms tumor, hepatoblastoma, and rhabdomyosarcoma.

PROCEDURE AND RESULTS

In this article, we describe an adolescent male with congenital asymmetry of the lower limbs who presented with a large poorly differentiated pelvic sarcoma. Conventional histologic, immunohistochemical, and ultrastructural studies of this tumor were insufficient for accurate subclassfication. However, positive staining for MyoD1 (a recently identified embryonically expressed marker of muscle differentiation) and LOH at the tyrosine hydroxylase locus of chromosome 11p15.5 by molecular analysis favored the diagnosis of embryonal rhabdomyosarcoma over an undifferentiated sarcoma.

CONCLUSIONS

This case stresses the importance of pursuing clinical findings when they occur in conditions with an increased risk of developing cancer, which in this case was asymmetry of a limb. Also illustrated by this patient is the need for early consideration of molecular diagnostic tests where available, to refine an uncertain pathologic diagnosis that may ultimately have an impact on treatment and prognosis.