Fluorescence In Situ Hybridisation (FISH) To Reveal Isochromosome 7q, i(7)(q10), in Hepatosplenic T-Cell Lymphoma (HSTCL).
Authors: Bernasconi Paolo , Dambruoso Irene , Boni Marina , Cavigliano Paola Maria , Giardini Ilaria , Zappatore Rita , Calatroni Silvia , Rocca Barbara , Astori Cesare , Castagnola Carlo , Lazzarino Mario 
Published: April 2020

We report two HSTCL patients who were studied with conventional cytogenetics (CC) and FISH on clinical diagnosis and during the follow-up to better understand the genetic events underlying this type of lymphoma.

They were a 21-year old male and a 44-year old woman who came to our clinic for evaluation because of B-symptoms. On physical examination they presented massive splenomegaly and hepatomegaly. A peripheral blood count revealed anemia and thrombocytopenia in one patient and anemia in the other. They both presented high lactic dehydrogenase levels. A bone marrow biopsy demonstrated that a malignant T-cell population constituted 30% of all marrow cells in one patient and entirely substituted normal hemopoiesis in the other. This malignant T-cell population was CD2+,CD3+,CD7+,CD56+,CD4−,CD5−,CD8−. In addition, the T-cell clone, which showed a sinusal localization, was TCRα/β + in one case and TCRγ/δ + in the other. The two patients underwent splenectomy and it was shown that the red pulp had been completely infiltrated by a malignant cell population identical to that present in the marrow of the two patients. Therefore, a diagnosis of α/β + and γ/δ+ HSTCL in stage IVB was made and the patients started treatment. The male succeeded in entering a complete remission (CR) of only three month duration and after a bone marrow relapse was unable to achieve a second CR. The female did not respond to chemotherapy and died of disease related complications.

CC and FISH studies were performed on bone marrow cells. CC discovered a normal chromosome pattern in the twenty metaphases obtained from the first patient, and an abnormal pattern in the eighteen mitotic cells obtained from the second whose karyotype was: 46,XX[7]/46,XX,i(7)(q10)[5]/47,XX,i(7)(q10),+i(7)(q10)[6]. FISH on mitotic and interphase cells was performed with the 7q31/CEP11 probe (Vysis) and the Bacterial Artificial Chromosome (BAC) probes RP11-79N1, RP11-299F5, RP11-1132K14, RP11-163M21 (kindly provided by the Wellcome Trust Sanger Institute, Cambridge UK and by the BACPAC Resources Children’s Hospital, Oakland, USA), which were localized on 7p15 and covered the HOXA cluster. The commercial probes were applied according to manufacturer’s guidelines. Hybridization procedures were carried out first with the BAC probes and subsequently with the commercial probes.

On clinical diagnosis a significant cell population with the aberrant pattern (1×7p/2×7cen/3×7q) corresponding to i(7)(q10) was discovered in 25% of marrow cells from the first patient and in 90% marrow cells from the second. Interestingly, in the first patient the percentage of cells displaying this pattern equalled the percentage of cells infiltrating the marrow on morphologic examination. However, when this patient relapsed we did not succeed in identifying any cell carrying the 1×7p/2×7cen/3×7q pattern (cut-off fixed at 2%), even if the percentage of malignant T-cells infiltrating the marrow was higher than on diagnosis. In addition, CC revealed an absolutely normal chromosome pattern leading us to hypothesize that a cryptic genetic event might have occurred.

In conclusion, our findings

further underscore the association between i(7)(q10) and HSTCL, suggest that the number of i(7)(q10) present in the malignant cell might reduce response to treatment, lead us to hypothesize that patients who relapse might develop a second more subtle genetic lesion.