Irradiated Blm-deficient mice are a highly tumor prone model for analysis of a broad spectrum of hematologic malignancies

Rare case of myelodysplastic syndrome with excess blasts 2 developing after adjuvant chemoradiotherapy for triple-negative breast cancer in a patient with Bloom syndrome

INTRODUCTION

Bloom syndrome (BS) is a rare autosomal recessive disorder caused by a loss-of-function mutation in the BLM gene encoding an RecQ helicase involved in DNA repair and maintenance of chromosomal stability. In patients with BS, significant sensitivity to both DNA-damaging chemotherapy (CT) and ionizing radiation complicates the management of neoplasms by exacerbating comorbidities and predisposing to toxicities and poor outcomes.

CASE REPORT

A 30-year-old female patient diagnosed with BS who presented with early-stage triple-negative breast cancer was treated with four cycles of doxorubicin (60 mg/m2) and cyclophosphamide (600 mg/m2) followed by weekly paclitaxel (80 mg/m2) for 12 weeks as the chemotherapy protocol and a total of 5000 cGy curative radiotherapy (RT). Due to pancytopenia 8 months after completion of therapy, bone marrow biopsy and aspiration were performed, and a diagnosis of myelodysplastic syndrome with excess blasts 2 (MDS-EB2) was made. Two courses of the azacitidine (75 mg/m2) protocol were administered every 28 days in the hematology clinic. Two weeks after CT the patient was transferred from the emergency department to the hematology clinic with the diagnosis of pancytopenia and febrile neutropenia. She died at the age of 33 due to sepsis that developed during follow-up.

CONCLUSION

Due to the rarity of BS, there is no prospective trial in patients with cancer and no evidence base upon which to design treatment programs. For these reasons, it is strongly recommended that patients receive multidisciplinary care, with precise assessment and discussion of the indication and an adequate dose of DNA-damaging agents such as chemotherapy and ionizing radiation.

Age of first cancer diagnosis and survival in Bloom syndrome

PURPOSE

This study aimed to describe the spectrum of cancers observed in Bloom Syndrome and the observed survival and age of first cancer diagnosis in Bloom syndrome as these are not well-defined.

METHODS

Data from the Bloom Syndrome Registry (BSR) was used for this study. Cancer history, ages of first cancer diagnosis, and ages of death were compiled from the BSR and analyzed.

RESULTS

Among the 290 individuals in the BSR, 155 (53%) participants developed 251 malignant neoplasms; 100 (65%) were diagnosed with 1 malignancy, whereas the remaining 55 (35%) developed multiple malignancies. Of the 251 neoplasms, 83 (33%) were hematologic and 168 (67%) were solid tumors. Hematologic malignancies (leukemia and lymphoma) were more common than any of the solid tumors. The most commonly observed solid tumors were colorectal, breast, and oropharyngeal. The cumulative incidence of any malignancy by age 40 was 83%. The median survival for all participants in the BSR was 36.2 years. There were no significant differences in time to first cancer diagnosis or survival by genotype among the study participants.

CONCLUSION

We describe the spectrum of cancers observed in Bloom syndrome and the observed survival and age of first cancer diagnosis in Bloom syndrome. We also highlight the significant differences in survival and age of diagnosis seen among different tumor types and genotypes.

Functions of BLM Helicase in Cells: Is It Acting Like a Double-Edged Sword?

DNA damage repair response is an important biological process involved in maintaining the fidelity of the genome in eukaryotes and prokaryotes. Several proteins that play a key role in this process have been identified. Alterations in these key proteins have been linked to different diseases including cancer. BLM is a 3′−5′ ATP-dependent RecQ DNA helicase that is one of the most essential genome stabilizers involved in the regulation of DNA replication, recombination, and both homologous and non-homologous pathways of double-strand break repair. BLM structure and functions are known to be conserved across many species like yeast, Drosophila, mouse, and human. Genetic mutations in the BLM gene cause a rare, autosomal recessive disorder, Bloom syndrome (BS). BS is a monogenic disease characterized by genomic instability, premature aging, predisposition to cancer, immunodeficiency, and pulmonary diseases. Hence, these characteristics point toward BLM being a tumor suppressor. However, in addition to mutations, BLM gene undergoes various types of alterations including increase in the copy number, transcript, and protein levels in multiple types of cancers. These results, along with the fact that the lack of wild-type BLM in these cancers has been associated with increased sensitivity to chemotherapeutic drugs, indicate that BLM also has a pro-oncogenic function. While a plethora of studies have reported the effect of BLM gene mutations in various model organisms, there is a dearth in the studies undertaken to investigate the effect of its oncogenic alterations. We propose to rationalize and integrate the dual functions of BLM both as a tumor suppressor and maybe as a proto-oncogene, and enlist the plausible mechanisms of its deregulation in cancers.

A Structural Guide to the Bloom Syndrome Complex

The Bloom syndrome complex is a DNA damage repair machine. It consists of several protein components which are functional in isolation, but interdependent in cells for the maintenance of accurate homologous recombination. Mutations to any of the genes encoding these proteins cause numerous physical and developmental markers as well as phenotypes of genome instability, infertility, and cancer predisposition. Here we review the published structural and biochemical data on each of the components of the complex: the helicase BLM, the type IA topoisomerase TOP3A, and the OB-fold-containing RMI and RPA subunits. We describe how each component contributes to function, interacts with each other, and the DNA that it manipulates/repairs.

In vivo functional screening for systems-level integrative cancer genomics

With the genetic portraits of all major human malignancies now available, we next face the challenge of characterizing the function of mutated genes, their downstream targets, interactions and molecular networks. Moreover, poorly understood at the functional level are also non-mutated but dysregulated genomes, epigenomes or transcriptomes. Breakthroughs in manipulative mouse genetics offer new opportunities to probe the interplay of molecules, cells and systemic signals underlying disease pathogenesis in higher organisms. Herein, we review functional screening strategies in mice using genetic perturbation and chemical mutagenesis. We outline the spectrum of genetic tools that exist, such as transposons, CRISPR and RNAi and describe discoveries emerging from their use. Genome-wide or targeted screens are being used to uncover genomic and regulatory landscapes in oncogenesis, metastasis or drug resistance. Versatile screening systems support experimentation in diverse genetic and spatio-temporal settings to integrate molecular, cellular or environmental context-dependencies. We also review the combination of in vivo screening and barcoding strategies to study genetic interactions and quantitative cancer dynamics during tumour evolution. These scalable functional genomics approaches are transforming our ability to interrogate complex biological systems.

Guidelines for the Optimization and Validation of In Situ Hybridization

As RNA in situ hybridization (ISH) moves into the mainstream lab and increasingly into clinical adoption and additional multiplexing techniques are developed to enable further RNA ISH identification, a set of guidelines on the validation of ISH is required. These guidelines include choice of methods, appropriate controls, and protocol optimization as well as a central core message of understanding the target, understanding the ISH technique, and using the most appropriate controlling mechanisms to enable reproducible and trustworthy data to be obtained.

Adenocarcinoma of the Right Colon in a Patient with Bloom Syndrome

Introduction. Bloom syndrome (BS) is an inherited disorder due to mutation in BLM gene. The diagnosis of BS should be considered in patients with growth retardation of prenatal onset, a photosensitive rash in a butterfly distribution over the cheeks, and an increased risk of cancer at an early age. Clinical manifestations also include short stature, dolichocephaly, prominent ears, micrognathia, malar hypoplasia and a high-pitched voice, immunodeficiency, type II diabetes, and hypogonadism associated with male infertility and female subfertility. The aim of this report is to describe case of patient with BS who developed adenocarcinoma of the cecum, successfully treated by right colectomy. Case Report. A 40-year-old man underwent colonoscopy to investigate the cause of his diarrhea, weight loss, and anemia. The patient knew that he was a carrier of BS diagnosed at young age. The colonoscopy showed an expansive and vegetating mass with 5.5 cm in diameter, located within the ascending colon. Histopathological analysis of tissue fragments collected during colonoscopy confirmed the presence of tubular adenocarcinoma, and he was referred for an oncological right colectomy. The procedure was performed without complications, and the patient was discharged on the fifth postoperative day. Histopathological examination of the surgical specimen confirmed the presence of a grade II tubular adenocarcinoma (stage IIA). The patient is currently well five years after surgery, without clinical or endoscopic signs of relapse in a multidisciplinary approach for the monitoring of comorbidities related to BS. Conclusion. Despite the development of colorectal cancer to be, a possibility rarely described the present case shows the need for early screening for colorectal cancer in all patients affected by BS.

Loss of Blm enhances basal cell carcinoma and rhabdomyosarcoma tumorigenesis in Ptch1+/- mice

Basal cell carcinomas (BCCs) have relative genomic stability and relatively benign clinical behavior but whether these two are related causally is unknown. To investigate the effects of introducing genomic instability into murine BCCs, we have compared ionizing radiation-induced tumorigenesis in Ptch1(+/-) mice versus that in Ptch1(+/-) mice carrying mutant Blm alleles. We found that BCCs in Ptch1(+/-) Blm(tm3Brd/tm3Brd) mice had a trend toward greater genomic instability as measured by array comprehensive genomic hybridization and that these mice developed significantly more microscopic BCCs than did Ptch1(+/-) Blm(+/tm3Brd) or Ptch1(+/-) Blm(+/+) mice. The mutant Blm alleles also markedly enhanced the formation of rhabdomyosarcomas (RMSs), another cancer to which Ptch1(+/)(-) mice and PTCH1(+/)(-) (basal cell nevus syndrome) patients are susceptible. Highly recurrent but different copy number changes were associated with the two tumor types and included losses of chromosomes 4 and 10 in all BCCs and gain of chromosome 10 in 80% of RMSs. Loss of chromosome 11 and 13, including the Trp53 and Ptch1 loci, respectively, occurred frequently in BCCs, suggesting tissue-specific selection for genes or pathways that collaborate with Ptch deficiency in tumorigenesis. Despite the quantitative differences, there was no dramatic qualititative difference in the BCC or RMS tumors associated with the mutant Blm genotype.