Medical students' self-perceived knowledge and clinical comfort with genetics in Pakistan.

Pakistan has a high rate of genetic disorders and neonatal mortality concurrent with noted lack of genetic counselors and geneticists. To meet the needs of the patient population, the responsibility of providing clinical genetic services falls on general and specialty physicians. However, their education regarding these essential services is not standardized in medical school curricula nor has it ever been evaluated. The purpose of this work is to describe the self-perceived knowledge, clinical comfort, and perspectives of Pakistani medical students toward their medical genetics' education. A web-based survey was distributed electronically to medical schools around the country. The survey comprised of four sections: (1) participant demographics, (2) self-perceived medical genetics knowledge, (3) level of comfort in applying genetic knowledge and skills, and (4) attitudes toward medical genetics education. Descriptive statistics and a one-way analysis of variance were used for data analysis. Medical students in years 3, 4, and 5 (n = 473) from 25 medical schools participated in this research representing medical education in four Pakistani provinces. Most medical students reported "minimal" to "basic" knowledge of genetic testing methodology (64.7%), cancer genetics (64.9%), prenatal genetic testing (63.02%), and treatment strategies for genetic disease (72.9%). A plurality of students (37%) reported they were uncomfortable with interpreting and communicating genetic test results to patients. Medical students also expressed dissatisfaction with their medical genetics (40%) and genetic counselors training (42%). The self-perceived knowledge and clinical comfort with genetics among Pakistani medical students was limited, especially regarding genetic testing. A significant portion (74.5%) expressed desire for additional genetics education during medical school to aid in their role as future physicians. It is important for physicians-in-training to have a solid understanding of genetic concepts, technologies, and genetic counseling to best support their patients. As endorsed by the participating medical students, this study supports inclusion of more robust genetics' education into Pakistan's medical school curricula.

Mycosis fungoides with epidermal mucinosis: a variant of mycosis fungoides with a spongiosis-like pattern.

BACKGROUND: The histopathologic diagnosis of mycosis fungoides (MF) has classically relied on the presence of atypical epidermotropic T-lymphocytes predominating over spongiosis. However, in some cases of MF, prominent epidermal mucinosis in a spongiosis-like pattern mimics a spongiotic dermatitis. To our knowledge, only one series in the literature has thus far recognized the presence of epidermal mucinosis in MF. METHODS: We evaluated 30 skin biopsies from 18 patients with the clinical diagnosis of MF, which fulfilled all histopathologic criteria for patch- or plaque-stage MF, but also showed epidermal mucinosis in a spongiosis-like pattern. A total of 15 specimens were studied by immunohistochemistry, and seven were tested for T-cell receptor (TCR) gene rearrangements. Twenty biopsies of spongiotic dermatitides were included as controls. RESULTS: We confirmed the presence of epidermal mucinosis in all 30 cases of MF with a spongiosis-like pattern based on histopathologic criteria and the colloidal iron stain for mucin. Immunohistochemistry in 15 specimens showed significant loss of pan-T-cell antigens CD5 (10/15) and CD7 (14/15); and TCR clonality was detected in 7 specimens from 6 patients, supporting the diagnosis of MF. CONCLUSIONS: We report helpful histopathologic criteria for distinguishing MF with epidermal mucinosis in a spongiosis-like pattern from spongiotic dermatitis.

Pitfalls of using polymerase chain reaction-based assays for JAK2 and CALR exon 9 variant testing in myeloproliferative neoplasms: Knowing when to go the extra mile!

OBJECTIVES: The BCR::ABL1 negative myeloproliferative neoplasms are sequentially tested for JAK2 p.V617F, followed by CALR exon 9 pathogenic variants. Historically, these variants were thought to be mutually exclusive. However, recent reports indicate coexisting JAK2 p.V617F and CALR exon 9 somatic variants. METHODS: Analysis of JAK2 p.V617F and CALR exon 9 variant was performed by polymerase chain reaction (PCR)-based assays. Subsequent testing was performed on the Genexus integrated sequencer (ThermoFisher) using the Oncomine myeloid assay GX v2. RESULTS: CALR exon 9 variants were positive in 3 cases, while 2 were positive for JAK2 p.V617F on PCR-based assays. Next-generation sequencing confirmed the JAK2 P.V617F status in all cases. CALR variants resulting in in-frame deletions were identified in 2 cases at a variant allele frequency of 52.16% and 50.91%, while the third case had an intronic CALR variant c.-48G>A at a variant allele frequency of 51.1%. Thus, CALR variants in all 3 cases were interpreted as potentially germline. Of the 228 cases that underwent JAK2 p.V617F and CALR cotesting in the past 2 years, only these 2 cases were positive for both JAK2 p.V617F and CALR exon 9 variants. CONCLUSIONS: These cases highlight the importance of understanding the pitfalls of molecular techniques in current practice.

Clinical validation of the Ion Torrent Oncomine Myeloid Assay GX v2 on the Genexus Integrated Sequencer as a stand-alone assay for single-nucleotide variants, insertions/deletions, and fusion genes: Challenges, performance, and perspectives.

OBJECTIVES: Myeloid neoplasms require comprehensive characterization of genetic abnormalities, including single-nucleotide variants, small insertions and deletions, and fusions and translocations for management. The Oncomine Myeloid Assay GX v2 (Thermo Fisher Scientific) analyzes 17 full genes, 28 hotspot genes, 30 fusion driver genes, and 5 expression genes. METHODS: The validation set included 192 DNA samples, 28 RNA samples, and 9 cell lines and contrived controls. The DNA and RNA were extracted from both peripheral blood and bone marrow. Library preparation, templating, and sequencing was performed on the fully automated Genexus Integrated Sequencer (Thermo Fisher Scientific). The sequencing data were analyzed by manual curation, default Oncomine filters and the Oncomine Reporter (Thermo Fisher Scientific). RESULTS: Of the 600 reference pathogenic DNA variants targeted by the assay, concordance was seen in 98.3% of unfiltered variant call format files. Precision and reproducibility were 100%, and the lower limit of detection was 2% variant allele frequency for DNA. Inability to detect variants in long homopolymer regions intrinsic to the Ion Torrent chemistry led to 7 missed variants; 100% concordance was seen with reference RNA samples. CONCLUSIONS: This extensive clinical validation of the Oncomine Myeloid Assay GX v2 on the Genexus Integrated Sequencer with its built-in bioinformatics pipeline and Ion Torrent Oncomine Reporter shows robust performance in terms of variant calling accuracy, precision, and reproducibility, with the advantage of a rapid turnaround time of 2 days. The greatest limitation is the inability to detect variants in long homopolymer regions.

Hypopigmented mycosis fungoides in childhood and adolescence: a long-term retrospective study.

Patients with hypopigmented mycosis fungoides (HMF) present at a younger age than those with classic MF. Our goal was to describe the clinical presentation, histopathologic features and long-term outcome in patients who developed HMF before the age of 21. It was observed that among 69 pediatric patients diagnosed with MF between 1992 and 2010, 50 had HMF. Thirty-five patients had clinical follow-up. There were 37 males and 32 females with a mean age of 13.6 years. Most patients were African American or Hispanic and presented with multiple hypopigmented patches. All biopsies showed epidermotropism of T-lymphocytes, whereas fibroplasia and lichenoid infiltrate were variable. All specimens tested were CD8+. Treatment modalities included topical steroids, narrow band ultraviolet B and psoralen and ultraviolet A. HMF patients were followed for <1-12 years. Most children responded to treatment, but recurrence rates were high. One patient progressed to plaque/tumor stage. Others did not progress; however, many were lost to follow-up. We present a large cohort of children with HMF and report on the features of disease and progression. A major difference in histology of HMF was lack of fibroplasia and lichenoid infiltrate, probably because of presentation in the early patch stage. Most patients have a waxing-and-waning course and relapse after discontinuation of therapy, requiring repetitive treatment.

Identifying the current status and future needs of clinical, educational, and laboratory genetics services in Pakistan: a web-based panel discussion.

While the prevalence of genetic disorders has been well documented in the Muslim-majority, low-socioeconomic country of Pakistan, the provision of medical genetic services remains limited and cost-prohibitive to the masses in the country. With the objective of identifying gaps in the provision of medical genetics services as perceived by the healthcare providers and the general public, the Pakistani Society of Medical Genetics and Genomics (PSMG) organized a needs assessment webinar on December 6, 2020, titled, "A Vibrant Discussion on the Current Status and Future Needs of Medical Genetic Services in Pakistan." The objectives of the webinar were (1) to explore the current availability of medical genetics services, (2) to identify areas in clinical genetics delivery models needed to improve the state of medical genetics in the country, and (3) to garner the interest in such provisions from the expert and lay audience. The webinar consisted of a moderator-led, structured interview of an expert panel including the following topics: (1) postgraduate clinical genetics and genetic counseling training programs, (2) medical genetics clinics and formal genetic counseling services), (3) clinical genetic testing and (4) patient support and advocacy groups. The webinar was followed by a short, web-based survey completed by 35 of the 60 attendees. The results of this survey indicated overwhelming support for establishing formal genetic counseling educational opportunities (91.6%) and increasing the availability of genetic testing (100%). This report further summarizes the opinions and recommendations of the panelists and the audience survey results.

PIK3CA-related overgrowth spectrum (PROS) presenting as isolated macrodactyly.

PIK3CA-related overgrowth spectrum (PROS) is a heterogeneous group of diseases, with varied clinical presentations ranging from isolated segmental overgrowths to megalencephaly and vascular malformations, all resulting from post-zygotic activating mutations in PIK3CA. Isolated macrodactyly of upper limb is extremely rare, accounting only for 0.9%-1% of all congenital anomalies of the upper limb. This report describes a case of congenital, isolated, nonprogressive macrodactyly of the right index finger and thumb, in an adult patient that was treated with debulking surgery. The microscopic features were compatible with lipomatosis of nerve. Due to the prompt and pertinent molecular testing, which identified a somatic PIK3CA variant, c.3140A > G, p.H1047R., the case was classified as a PROS. The availability of mTOR inhibitors offers additional treatment possibilities in cases with progressive disease. This case report highlights the importance of molecular testing to identify PROS, to further the knowledge of this continually expanding entity.

Ameloblastoma with adenoid features: Case report with cyto-histopathologic correlation and molecular findings.

Ameloblastomas are benign but locally aggressive odontogenic tumors that commonly present as expansile lesions in the tooth-bearing areas. Fine-needle aspiration (FNA) biopsies of ameloblastomas are rare in clinical practice, and only a handful of case reports and series have described their cytologic features. We present the case of a 70-year-old woman with a large and disfiguring maxillary sinus soft tissue mass sampled via transcutaneous FNA. Aspirate smears were composed of small clusters of cohesive and monotonous basaloid cells. The accompanying cellblock showed similar clusters of basaloid cells in gland-like, or "adenoid," configurations, eliciting a differential diagnosis that included sinonasal and salivary gland neoplasms. Excisional surgery material was consistent with ameloblastoma with adenoid morphology. Next-generation sequencing (NGS) analysis demonstrated FGFR2 and SMO pathogenic variants. This case exemplifies several uncommonly described features of ameloblastomas in cytology, including cyto-histologic correlation, adenoid morphology, and NGS findings. Awareness of the cytologic features of this neoplasm are important for cytopathologists confronted with maxillary sinus lesions.

Karyotypic complexity, TP53 pathogenic variants, and increased number of variants on Next-Generation Sequencing are associated with disease progression in a North American Adult T-Cell Leukemia/Lymphoma cohort.

INTRODUCTION: Adult T-Cell Leukemia/Lymphoma (ATLL) is an aggressive T-cell malignancy without known characteristic cytogenetic abnormalities. Recurrent mutations in TP53, APC, and epigenetic and histone-modifying genes have been identified in North American ATLL. Their roles in disease progression are not yet fully elucidated. METHODS: We studied the cytogenetic and Next-Generation Sequencing (NGS) findings of the North American ATLL cohort at our institution and compared the findings with Japanese and other North American cohorts. We also analyzed the genetic variants in TP53, APC, and histone-modifying genes and investigated the impact of their mutations on the number of mutations via NGS in ATLL. RESULTS: Cases with more than 6 chromosomal breaks (n = 13) had significantly shorter overall survival compared to cases with fewer chromosomal breaks (n = 7) (P = .0007). Cases with breaks on chromosome 3q (n = 4) exhibited worse survival compared to the rest of the cases (n = 16) (P = .012). Chromosomal abnormalities on 3q, 14q, 1q, 1p, and 17q are likely primary changes in ATLL based on frequency and association with prognosis. The average number of mutations via NGS was significantly higher in cases with mutations in TP53 (n = 8) (P = .020) as well as APC (n = 6) (P = .024) compared to cases without mutations in these genes. All TP53 variants were pathogenic missense and truncating mutations in COSMIC database. CONCLUSION: Cytogenetic and NGS methods are useful tools to monitor disease progression in indolent ATLL and assess prognosis in aggressive ATLL.

Syndromic thrombocytopenia and predisposition to acute myelogenous leukemia caused by constitutional microdeletions on chromosome 21q.

Several lines of evidence support the presence of dosage-sensitive genes on chromosome 21 that regulate leukemogenesis and hematopoiesis. We report a detailed clinical and molecular characterization of 3 patients with chronic thrombocytopenia caused by distinct constitutional microdeletions involving chromosomal region 21q22.12. The patients exhibited growth restriction, dysmorphic features, and developmental delays. One patient developed acute myelogenous leukemia (AML) at 6 years of age. All 3 deletions included the RUNX1, CLIC6, DSCR, and KCNE1 genes. Our data provide additional support for the role of RUNX1 haploinsufficiency in megakaryopoiesis and predisposition to AML. The leukemic clone had trisomy 21 resulting from duplication of chromosome 21 containing the RUNX1 deletion. This shows that genes other than RUNX1 must also play a role in AML associated with trisomy 21. We recommend that children with syndromic thrombocytopenia have clinical array-comparative genomic hybridization analysis and appropriate cytogenetic studies to facilitate our ability to provide a definitive diagnosis.

Overexpression of ZNF342 by juxtaposition with MPO promoter/enhancer in the novel translocation t(17;19)(q23;q13.32) in pediatric acute myeloid leukemia and analysis of ZNF342 expression in leukemia.

We report a novel translocation t(17;19)(q22;q13.32) found in 100% of blast cells from a pediatric acute myeloid leukemia (AML) patient. Fluorescence in situ hybridization and vectorette polymerase chain reaction were used to precisely map the chromosomal breakpoint located on the derivative chromosome 17 at 352 bp 5' of MPO, encoding myeloperoxidase a highly expressed protein in myeloid cells, and 2,085 bp 5' of ZNF342 on 19q, encoding a transcription factor expressed in human stem cells and previously implicated in mouse models of leukemia. Analysis of RNA levels from the patient sample revealed significant overexpression of ZNF342, potentially contributing to AML formation. This is the first report of a translocation in myeloid leukemia occurring only in the promoter/enhancer regions of the two genes involved, similar to translocations commonly found in lymphoid malignancies. Analysis of ZNF342 protein levels in a large dataset of leukemia samples by reverse phase protein array showed that higher levels of ZNF342 expression in acute lymphoblastic leukemia was associated with poorer outcome (P = 0.033). In the myeloid leukemia samples with the highest ZNF342 expression, there was overrepresentation of FLT3 internal tandem duplication (P = 0.0016) and AML subtype M7 (P = 0.0002). Thus, overexpression of ZNF342 by translocation or other mechanisms contributes to leukemia biology in multiple hematopoietic compartments.

De novo mosaic and partial monosomy of chromosome 21 in a case with superior vena cava duplication.

BACKGROUND: Full or partial monosomy of chromosome (chr) 21 is a very rare abnormal cytogenetic finding. It is characterized by variable sizes and deletion breakpoints on the long arm (q) of chr 21 that lead to a broad spectrum of phenotypes that include an increased risk of birth defects, developmental delay and intellectual deficit. CASE PRESENTATION: We report a 37-year-old G1P0 woman initially screened by non-invasive prenatal testing with no positive findings that was followed by an 18-week anatomy scan with a fetal finding of duplication of the superior vena cava (SVC). The medical and family history was otherwise uneventful. After appropriate genetic counseling, amniocentesis was performed to evaluate suspected chromosomal anomalies. CONCLUSIONS: Interphase fluorescent in situ hybridization revealed loss of one chr 21 signal that was further delineated by chromosomal microarray analysis on uncultured amniocytes as a terminal 10 Mb deletion on chr 21q. Karyotype and microarrays on cultured amniocytes showed two cell lines for a mosaic 21q terminal deletion and monosomy 21. The combined molecular cytogenetics results reported following the ISCN 2016 guideline as mos 46,XX,del(21)(q22)dn[20]/45,XX,-21dn[10].nuc ish(D21S342/D21S341/D21S259x1)[100].arr[GRCh37] 21q11.2q22.12(15412676_36272993)x1~2,21q22.12q22.3(36431283_47612400)x1. Parental chromosomal analysis revealed normal karyotypes. Thus, this was a de novo mosaic full and partial monosomy of chr 21 in a case with SVC duplication. Despite the association of congenital heart disease with monsomy 21 we could not find any published literature or online databases for this cytogenetic abnormality. The patient terminated the pregnancy following the abnormal molecular cytogenetic results due to the possible challenges the baby would face if carried to term.

Enhanced Carrier Screening for Spinal Muscular Atrophy: Detection of Silent (SMN1: 2 + 0) Carriers Utilizing a Novel TaqMan Genotyping Method.

BACKGROUND: Individuals whose copies of the survival motor neuron 1 (SMN1) gene exist on the same chromosome are considered silent carriers for spinal muscular atrophy (SMA). Conventional screening for SMA only determines SMN1 copy number without any information regarding how those copies are arranged. A single nucleotide variant (SNV) rs143838139 is highly linked with the silent carrier genotype, so testing for this SNV can more accurately assess risk to a patient of having an affected child. METHODS: Using a custom-designed SNV-specific Taqman genotyping assay, we determined and validated a model for silent-carrier detection in the laboratory. RESULTS: An initial cohort of 21 pilot specimens demonstrated results that were 100% concordant with a reference laboratory method; this cohort was utilized to define the reportable range. An additional 177 specimens were utilized for a broader evaluation of clinical validity and reproducibility. Allelic-discrimination analysis demonstrated tight clustering of genotype groupings and excellent reproducibility, with a coefficient of variation for all genotypes ranging from 1% to 4%. CONCLUSION: The custom-developed Taqman SNV genotyping assay we tested provides a rapid, accurate, and cost-effective method for routine SMA silent-carrier screening and considerably improves detection rates of residual risk for SMA carriers.

Molecular monitoring of 8p11 myeloproliferative syndrome in an infant.

The 8p11 myeloproliferative syndrome is a rare hematologic malignancy derived from a pluripotent hematopoietic stem cell associated with rearrangements involving the fibroblast growth factor receptor 1 (FGFR1) gene located on chromosome 8p11. The most common translocation, t(8;13) (p11;q13), results in a ZNF198-FGFR1 fusion gene and constitutively active FGFR1 tyrosine kinase activity. Typical pathologic findings include myeloid hyperplasia, lymphadenopathy, precursor T-lymphoblastic lymphoma, and eosinophilia. The disease is usually associated with an aggressive course and progression to acute myeloid leukemia is frequent. We report here the first case of 8p11 myeloproliferative syndrome in an infant and demonstrate the value of molecular testing in the diagnosis and minimal disease monitoring of this rare disease.

Clinical utility of array comparative genomic hybridization for detection of chromosomal abnormalities in pediatric acute lymphoblastic leukemia.

BACKGROUND: Accurate detection of recurrent chromosomal abnormalities is critical to assign patients to risk-based therapeutic regimens for pediatric acute lymphoblastic leukemia (ALL). PROCEDURE: We investigated the utility of array comparative genomic hybridization (aCGH) for detection of chromosomal abnormalities compared to standard clinical evaluation with karyotype and fluorescent in situ hybridization (FISH). Fifty pediatric ALL diagnostic bone marrows were analyzed by bacterial artificial chromosome (BAC) array and findings compared to standard clinical evaluation. RESULTS: Sensitivity of aCGH was 79% to detect karyotypic findings other than balanced translocations, which cannot be detected by aCGH because they involve no copy number change. aCGH also missed abnormalities occurring in subclones constituting less than 25% of cells. aCGH detected 44 additional abnormalities undetected or misidentified by karyotype with 21 subsequently validated by FISH, including abnormalities in 4 of 10 cases with uninformative cytogenetics. aCGH detected concurrent terminal deletions of both 9p and 20q in three cases, in two of which the 20q deletion was undetected by karyotype. A narrow region of loss at 7p21 was detected in two cases. CONCLUSIONS: aCGH detects the majority of karyotypic findings other than balanced translocations, and may provide key prognostic information in the approximately 35% of cases with uninformative cytogenetics.

Clear cell sarcoma of soft tissue: diagnostic utility of fluorescence in situ hybridization and reverse transcriptase polymerase chain reaction.

A 7-year-old girl presented with pain and progressive swelling on the left plantar surface. Biopsy of a 2.5 cm mass showed nests of large round to oval neoplastic cells with abundant amphophilic to clear cytoplasm, prominent nucleoli and high mitotic activity. Occasional cells showed spindled morphology. Infrequent melanin pigment was present. Melanocytic markers (HMB45, S-100) were diffusely positive. A diagnosis of clear cell sarcoma of soft tissue (CCSS) was made, and the mass was re-excised with negative margins. 28 months later, a 1.0 cm pulmonary nodule was identified and wedge excision showed metastatic CCSS. Cytogenetics showed a complex karyotype (unbalanced translocation der(12;14)(q10;q10), additional chromosome 22 material of unknown origin). Although the CCSS translocation t(12;22)(q13;q12) was not identified, EWSR1 gene rearrangement was detected by fluorescence in situ hybridization (FISH). Reverse transcription polymerase chain reaction (RT-PCR) showed an EWS-ATF1 fusion transcript, confirmed by direct sequencing. CCSS requires differentiation from malignant melanoma, because of overlapping clinical presentations, sites of involvement, histomorphology, immunocytochemical profiles and ultrastructure. In many circumstances, definitive diagnosis is only possible with confirmation of the CCSS-defining translocation.

C/EBPbeta suppression by interruption of CUGBP1 resulting from a complex rearrangement of MLL.

Translocations involving the mixed-lineage leukemia gene (MLL) confer a poor prognosis in acute leukemias. In t(1;11)(q21;q23), MLL is fused reciprocally with AF1q. Here we describe a t(1;11)(q21;q23) with a secondary event involving insertion of the telomeric portion of MLL into the p arm of chromosome 11 (11p11). We show that this latter event interrupts the CUG triplet repeat binding protein-1 (CUGBP1) gene, a translational enhancer of C/EBPbeta. We then showed that these cells have reduced expression of CUGBP1 and C/EBPbeta when compared to other AML blasts. This is the first report to describe insertional disruption of the CUGBP1 gene and to suggest a role for the CUGBP1-C/EBPbeta pathway in leukemogenesis.

Cloned transchromosomic calves producing human immunoglobulin.

Human polyclonal antibodies (hPABs) are useful therapeutics, but because they are available only from human donors, their supply and application is limited. To address this need, we prepared a human artificial chromosome (HAC) vector containing the entire unrearranged sequences of the human immunoglobulin (hIg) heavy-chain (H) and lambda (lambda) light-chain loci. The HAC vector was introduced into bovine primary fetal fibroblasts using a microcell-mediated chromosome transfer (MMCT) approach. Primary selection was carried out, and the cells were used to produce cloned bovine fetuses. Secondary selection was done on the regenerated fetal cell lines, which were then used to produce four healthy transchromosomic (Tc) calves. The HAC was retained at a high rate (78-100% of cells) in calves and the hIg loci underwent rearrangement and expressed diversified transcripts. Human immunoglobulin proteins were detected in the blood of newborn calves. The production of Tc calves is an important step in the development of a system for producing therapeutic hPABs.

Loss of heterozygosity occurs via mitotic recombination in Trp53+/- mice and associates with mammary tumor susceptibility of the BALB/c strain.

Loss of heterozygosity (LOH) occurs commonly in cancers causing disruption of tumor suppressor genes and promoting tumor progression. BALB/c-Trp53(+/-) mice are a model of Li-Fraumeni syndrome, exhibiting a high frequency of mammary tumors and other tumor types seen in patients. However, the frequency of mammary tumors and LOH differs among strains of Trp53(+/-) mice, with mammary tumors occurring only on a BALB/c genetic background and showing a high frequency of LOH, whereas Trp53(+/-) mice on a 129/Sv or (C57BL/6 x 129/Sv) mixed background have a very low frequency of mammary tumors and show LOH for Trp53 in only approximately 50% of tumors. We have performed studies on tumors from Trp53(+/-) mice of several genetic backgrounds to examine the mechanism of LOH in BALB/c-Trp53(+/-) mammary tumors. By Southern blotting, 96% (24 of 25) of BALB/c-Trp53(+/-) mammary tumors displayed LOH for Trp53. Karyotype analysis indicated that cells lacking one copy of chromosome 11 were present in all five mammary tumors analyzed but were not always the dominant population. Comparative genomic hybridization analysis of these five tumors indicated either loss or retention of the entire chromosome 11. Thus chromosome loss or deletions within chromosome 11 do not account for the LOH observed by Southern blotting. Simple sequence length polymorphism analysis of (C57BL/6 x BALB/c) F1-Trp53(+/-) mammary tumors showed that LOH occurred over multiple loci and that a combination of maternal and paternal alleles were retained, indicating that mitotic recombination is the most likely mechanism of LOH. Nonmammary tumors of BALB/c mice also showed a high frequency of LOH (22 of 26, 85%) indicating it was not a mammary tumor specific phenomenon but rather a feature of the BALB/c strain. In (C57BL/6 x BALB/c) F1-Trp53(+/-) mice LOH was observed in 93% (13 of 14) of tumors, indicating that the high frequency of LOH was a dominant genetic trait. Thus the high frequency of LOH for Trp53 in BALB/c-Trp53(+/-) mammary tumors occurs via mitotic recombination and is a dominant genetic trait that associates with the occurrence of mammary tumors in (C57BL/6 x BALB/c) F1-Trp53(+/-) mice. These results further implicate double-strand DNA break repair machinery as important contributors to mammary tumorigenesis.

Overexpression of MAGE/GAGE genes in paclitaxel/doxorubicin-resistant human cancer cell lines.

Previous studies directed at identifying paclitaxel resistance genes in a paclitaxel-resistant subclone of the human ovarian cancer cell line SKOV-3 identified a novel cancer testis antigen, Taxol resistance-associated gene 3 (TRAG-3). Because investigation suggested that TRAG-3, located on chromosome Xq28, does not directly participate in the paclitaxel-resistant phenotype, it was hypothesized that TRAG-3 might be linked to a neighboring gene that is directly involved in the drug-resistant phenotype, or alternatively, overexpression of TRAG-3 might be attributable to coregulation with other cancer testis antigens. To distinguish between these two hypotheses, expression of the genes that flank TRAG-3 was evaluated, namely the Centrin 2 gene and several members of the MAGE gene cluster. Northern analysis demonstrates overexpression of MAGE2 but not Centrin 2. Extension of this analysis to other neighboring and non-neighboring representative cancer testis antigens reveals overexpression of MAGE3, MAGE6, MAGE11, and MAGE12, as well as GAGE-2, GAGE-4, GAGE-5, GAGE-6, and GAGE-7 (clustered on Xp11) in SKOV-3(TR), as compared with SKOV-3. In addition, Affymetrix-based analysis of gene expression in SKOV-3 subclones with variable paclitaxel resistance demonstrates MAGE gene overexpression occurs early in the development of the paclitaxel-resistant phenotype, whereas GAGE gene overexpression occurs somewhat later. Evaluation of additional breast and ovarian cancer cell lines reveals MAGE/GAGE overexpression in both paclitaxel- and doxorubicin-resistant cell lines, whereas gemcitabine-resistant subclones of several ovarian cancer cell lines, including SKOV-3(GR), reveals no change in MAGE/GAGE expression. To determine whether MAGE gene overexpression contributes directly to the drug-resistant phenotype, MAGE2 or MAGE6, cDNA was introduced into the paclitaxel-sensitive human ovarian cancer cell line OVCAR8. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cytotoxicity analysis of both MAGE2 and MAGE6 transfectants demonstrates a 4-fold increase in resistance to paclitaxel and 2-fold increase in resistance to doxorubicin but not to other drugs, such as topotecan and cisplatin, through a nonmultidrug resistance-1 mechanism. MAGE2 or MAGE6 overexpression also induces a growth advantage in OVCAR8-transfected cells. These studies suggest that the in vitro acquisition of paclitaxel and doxorubicin resistance can be associated with increased expression of a variety of both neighboring and non-neighboring cancer testis antigens genes. This does not appear to be a consequence of random genetic instability or genomic amplification of the X chromosome. These antigens, because of limited expression in normal tissues, may be suitable targets for immunotherapy and novel therapeutic strategies in the treatment of chemotherapy-resistant epithelial tumors.