Carla B. Ripamonti

Trisomy 4 Leading to Duplication of a Mutated KIT Allele in Acute Myeloid Leukemia with Mast Cell Involvement

A G-->T transversion at nucleotide 2467 of the c-KIT gene leading to Asp816-->Tyr (D816Y) substitution in the phosphotransferase domain has been previously identified in a patient with rapidly progressing AML-M2 and mast cell involvement; the patients blasts had a 47,XY, +4,t(8;21)(q22;q22) karyotype. Herein we confirm the simultaneous presence of both major chromosomal changes by multicolor fluorescence in situ hybridization (FISH) on interphase CD34+ mononuclear cells. By setting up culture leukemic blasts, spontaneous differentiation of adherent cells with mast-cell like features was proved by histochemical and immunoenzymatic analyses. Fluorescence in situ hybridization evidence of trisomy 4 confirmed the origin of differentiated cells from the leukemic blasts. Semiquantitative polymerase chain reaction (PCR) and phosphoimage densitometry of wild-type and mutated KIT alleles on bone marrow blasts made it possible to demonstrate that chromosome 4 trisomy led to a double dosage of the mutated KIT allele. This finding, and that of trisomy 7 and MET mutation in hereditary renal carcinoma represent the only cases of human tumors in which an increased number of chromosomes carrying an oncogene activated by point mutation have been detected.

Molecular genetics of male infertility: Stem cell factor/c-kit system

PROBLEM: Infertility, affects about 5% of human males and genetic factors are recognized in approximately 30% of them. The mouse represents a good model to study autosomal genes that might play a role in spermatogenesis. In mice, mutations in the c‐kit gene and in the gene encoding stem cell factor (SCF) cause pleiotropic defects among which sterility. A possible involvement of the SCF/c‐kit system in human spermatogenesis was investigated.

Total serum tryptase: a predictive marker for KIT mutation in acute myeloid leukemia.

Human tryptase is a serine protease expressed in mast-cells. We previously observed that AML blast cells, cultured in vitro from a KIT D816Y patient, give rise to adherent cells with mast-cell like phenotype and tryptase was released in the serum-free medium. To correlate total serum tryptase (ts-try) levels with cytogenetic features and KIT mutational status, we analyzed serum samples from AML patients at diagnosis. In 70 out of 155 patients (45%) we detected elevated ts-try (>15 ng/mL), significantly linked to t(8;21) (P < .001) and inv(16) (P = .007). In patients that achieved complete remission the ts-try decreased to normal values. In 75 patients screened for KIT mutation, we found a clear relationship between elevated ts-try and mutated patients with t(8;21) (P < .001). In conclusion, we propose that checking for ts-try at diagnosis of AML may be a simple tool to select patients to be addressed to KIT mutation screening.

Survey of gynecological carcinosarcomas in families with breast and ovarian cancer predisposition

Carcinosarcomas (CSs) are biphasic neoplasms composed of high grade, malignant, epithelial and mesenchymal elements. The incidence of gynecological CSs (GCSs) is 0.4/100,000 women per year. Patients affected with GCSs have been occasionally reported in Hereditary Breast Ovarian Cancer (HBOC) families, including a few cases with pathogenic variants in BRCA1/BRCA2 genes. The prevalence and the association of GCSs in HBOC families have not been systematically investigated. Thus, we searched for families with GCSs in the HBOC registry of the National Cancer Institute of Milan. Eleven families, including four BRCA1-positive and four BRCA2-positive, presented a case of GCS. In the three BRCA1-mutated patients for whom surgical specimens were available, DNA fragment and sequencing analyses revealed the loss of the constitutionally wild-type BRCA1 allele. All tumors presented also TP53 mutations and stained positive for the expression of the protein product by immunohistochemistry. Our results suggest that GCSs may be found not infrequently in HBOC families and assimilate the analyzed CSs to BRCA1-related breast/ovarian carcinomas, where the above findings are frequently observed. Exploring the role of BRCA genes in prospective unselected series of GCSs might improve the knowledge of the genesis of these malignancies and guide the proposition of prophylactic surgery and targeted therapy.