Advances in the Biology of Acute Lymphoblastic Leukemia-From Genomics to the Clinic

Controversies in the Treatment of Adolescents and Young Adults with Philadelphia Chromosome-Negative B-Cell Acute Lymphoblastic Leukemia

PURPOSE OF THE REVIEW

The incidence of acute lymphoblastic leukemia (ALL) has been increasing steadily in the adolescent and young adult (AYA) population. In this review article focused on the management of AYAs with Philadelphia chromosome-negative (Ph-) B-ALL, we examine topics of clinical interest and identify areas of controversy in need of further investigation.

RECENT FINDINGS

We explore four areas of active investigation: pediatric-inspired front-line treatment regimens, the optimal time of measurable residual disease (MRD) assessment, the role of hematopoietic stem cell transplant and the optimal salvage therapy for relapsed/refractory B-ALL in AYAs. There has been rapid advancement in the management of ALL in the AYA patient population, which has resulted in improved outcomes. We must build on the successes by continuing to promote multi-center innovative clinical research with clinical trial populations reflecting the AYA ALL patient spectrum. The incorporation of novel targeted immunotherapy into front-line treatment will be transformative and redefine treatment paradigms in the coming years.

Ethical and Analytic Challenges With Genomic Sequencing of Relapsed Hematologic Malignancies Following Allogeneic Hematopoietic Stem-Cell Transplantation

The implementation of precision medicine and next-generation sequencing technologies in the field of oncology is a novel approach being more widely studied and used in cases of high-risk primary and recurrent malignancies. Leukemias are the second most common cause of cancer-related mortality in children and the sixth most in adults. Relapsed leukemia represents a major component of the population that may benefit from genomic sequencing. However, ethical and analytic challenges arise when considering sequencing of biologic samples obtained from patients with relapsed leukemia following allogeneic hematopoietic stem-cell transplantation. Blood from the recipient after transplantation would include donor-derived cells and thus, genomic sequencing of recipient blood will interrogate the donor germline in addition to the somatic genetic profile of the leukemia cells and the recipient germline. This is a situation for which the donor will not have typically provided consent and may be particularly problematic if actionable secondary or incidental findings related to the donor are uncovered. We present the challenges raised in this scenario and provide strategies to mitigate this risk.

Adolescent and Young Adult Cancer Biology

Adolescent and young adult (AYA) patients with cancer have not attained the same improvements in overall survival as either younger children or older adults. One possible reason for this disparity may be that the AYA cancers exhibit unique biologic characteristics, resulting in differences in clinical and treatment resistance behaviors. Our current understanding of the unique biological/genomic characteristics of AYA cancers is limited. However, there has been some progress that has provided clues about the biology of AYA cancers. We here review the latest findings in the area of AYA cancer biology and discuss what is required to advance the field for the more effective treatment of this patient population.

Disparities in Adolescents and Young Adults With Cancer

BACKGROUND

Cancer care for adolescents and young adults (AYAs) focuses on the care of patients aged 15 to 39 years. Historically, this group has favorable outcomes based on a preponderance of diagnoses such as thyroid cancers and Hodgkin lymphoma. Improvements in outcomes among the AYA population have lagged behind compared with younger and older populations.

METHODS

We discuss and review recent progress in AYA patient care and highlight remaining disparities that exist, including financial disadvantages, need for fertility care, limited clinical trial availability, and other areas of evolving AYA-focused research.

RESULTS

Survival rates have not improved for this age group as they have for children and older adults. Disparities are present in the AYA population and have contributed to this lack of progress.

CONCLUSIONS

Recognizing disparities in the care of AYAs with cancer has led many medical specialty disciplines to improve the lives of these patients through advocacy, education, and resource development. Research addressing barriers to clinical trial enrollment in this population, quality-of-life issues, and the improvement of survivorship care is also under way.

Increased incidence of FBXW7 and POLE proofreading domain mutations in young adult colorectal cancers

BACKGROUND

The incidence and outcomes of patients with colorectal cancer (CRC) varies by age. Younger patients tend to have sporadic cancers that are not detected by screening and worse survival. To understand whether genetic differences exist between age cohorts, the authors sought to characterize unique genetic alterations in patients with CRC.

METHODS

In total, 283 patients who were diagnosed with sporadic CRC between 1998 and 2010 were identified and divided by age into 2 cohorts-ages ≤45 years (the younger cohort) and ≥65 years (the older cohort)-and targeted exome sequencing was performed. The Fisher exact test was used to detect differences in mutation frequencies between the 2 groups. Whole exome sequencing was performed on 21 additional younger patient samples for validation. Findings were confirmed in The Cancer Genome Atlas CRC data set.

RESULTS

In total, 246 samples were included for final analysis (195 from the older cohort and 51 from the younger cohort). Mutations in the FBXW7 gene were more common in the younger cohort (27.5% vs 9.7%; P = .0022) as were mutations in the proofreading domain of polymerase ε catalytic subunit (POLE) (9.8% vs 1%; P = .0048). There were similar mutation rates between cohorts with regard to TP53 (64.7% vs 61.5%), KRAS (43.1% vs 46.2%), and APC (60.8% vs 73.8%). BRAF mutations were numerically more common in the older cohort, although the difference did not reach statistical significance (2% vs 9.7%; P = .082).

CONCLUSIONS

In this retrospective study, a unique genetic profile was identified for younger patients who have CRC compared with patients who are diagnosed at an older age. These findings should be validated in a larger study and could have an impact on future screening and treatment modalities for younger patients with CRC. Cancer 2016. © 2016 American Cancer Society. Cancer 2016;122:2828-2835. © 2016 American Cancer Society.

Oligo-based aCGH analysis reveals cryptic unbalanced der(6)t(X;6) in pediatric t(12;21)-positive acute lymphoblastic leukemia

Secondary chromosomal aberrations are necessary for development of overt leukemia in t(12;21)/ETV6-RUNX1-positive acute lymphoblastic leukemia (ALL). Conventional cytogenetic analysis supplemented with locus-specific FISH analyses is gold standard to detect important clonal aberrations in this disease group. However, adequate chromosome banding analysis may often be hampered by poor chromosome morphology and banding patterns in pediatric ALL cases, which may hinder identification of possible clinical important additional chromosomal aberrations. We used oligo-based high-resolution aCGH (oaCGH) analysis as an adjunct tool to enhance conventional cytogenetic analysis in pediatric acute B-cell lymphoblastic leukemia in a prospective single center study during a 4-year period (2012-2015). In a consecutive series of 45 pediatric B-ALLs, we identified eight patients with t(12;21)/ETV6-RUNX1 fusion by FISH analysis. In three of the patients, oaCGH analysis revealed concurrent Xq duplication and 6q deletion, which was cryptic by G-banded analysis. FISH analyses with whole chromosome painting probes confirmed the imbalances and showed an unbalanced translocation der(6)t(X;6) in all three patients. A search in the literature revealed two additional pediatric patients with cryptic der(6)t(X;6) in t(12;21)-positive ALLs. No common break points on Xq or 6q could be determined between the five patients. This study highlights the importance of oaCGH analysis as an adjunct cytogenetic tool to detect cryptic chromosomal aberrations. Further, the study adds to understanding the full spectrum of secondary chromosomal aberrations in the very common t(12;21)-positive pediatric ALL disease group. We suggest that the unbalanced der(6)t(X;6), which is cryptic to conventional cytogenetics, is a non-random secondary event in this disease group. It might be that the specific combination of concurrent Xq duplication and 6q-deletion results in gain of possible oncogenes on Xq and loss of possible tumor suppressor genes on 6q that are important for the leukemic propagation of t(12;21)-positive hematopoietic cells in a subset of ALLs.

Biologic and clinical characteristics of adolescent and young adult cancers: Acute lymphoblastic leukemia, colorectal cancer, breast cancer, melanoma, and sarcoma

Adolescent and young adult (AYA) patients with cancer have not attained the same improvements in overall survival as either younger children or older adults. One possible reason for this disparity may be that the AYA cancers exhibit unique biologic characteristics, resulting in differences in clinical and treatment resistance behaviors. This report from the biologic component of the jointly sponsored National Cancer Institute and LiveStrong Foundation workshop entitled "Next Steps in Adolescent and Young Adult Oncology" summarizes the current status of biologic and translational research progress for 5 AYA cancers; colorectal cancer breast cancer, acute lymphoblastic leukemia, melanoma, and sarcoma. Conclusions from this meeting included the need for basic biologic, genomic, and model development for AYA cancers as well as translational research studies to elucidate any fundamental differences between pediatric, AYA, and adult cancers. The biologic questions for future research are whether there are mutational or signaling pathway differences (for example, between adult and AYA colorectal cancer) that can be clinically exploited to develop novel therapies for treating AYA cancers and to develop companion diagnostics.

How can we improve on the already impressive results in pediatric ALL?

The past 70 years have seen childhood acute lymphoblastic leukemia move from a fatal disease with a survival of barely 4 months to a curable disease in >85% of patients. It has become clear that as treatment has intensified, more children are cured but at the expense of increased toxicity which for some can cause significant long-term morbidity and even mortality. The drive in more recent years has been to identify sensitive markers of disease and response to treatment to allow a reduction in therapy in those who do not require it and more intensive treatment in those who do. Clinical characteristics have been used to stratify patients into different risk groups and this, coupled with following response at a molecular level, has done much to tailor treatment to the patient. Considerable research has been focused on the molecular characteristics of the leukemia itself to elucidate the biologic mechanisms underlying both the disease and the comparative or absolute resistance of some types of leukemia. These molecular markers can also act as targets for novel therapies, which require newer trial methodologies to prove their utility. There has been less focus on the biology of the patient but it is clear that some patients are more susceptible to adverse events and toxicities than others. Through the use of pharmacogenomics, modification to therapy may be appropriate in certain patients based on their genetic profile. As novel therapies become available, suitable controlled trials in children are essential for their safe use in this population and will ensure that children are not denied timely access to advances in treatment.

Targeting Suppressor of Variegation 3-9 Homologue 2 (SUV39H2) in Acute Lymphoblastic Leukemia (ALL)

Although recent progress in understanding the biology and optimizing the treatment of acute lymphoblastic leukemia (ALL) has improved cure rates of childhood ALL to nearly 90%, the cure rate in adult ALL remains less than 50%. The poor prognosis in adult ALL has in part been attributed to larger proportion of high-risk leukemia showing drug resistance. Thus, identifying novel therapeutic targets in ALL is needed for further improvements in treatment outcomes of adult ALL. Genetic aberration of chromatin-modifying molecules has been recently reported in subtypes of ALL, and targeting components of chromatin complexes has shown promising efficacy in preclinical studies. Suppressor of variegation 3-9 homologue 2 (SUV39H2), also known as KMT1B, is a SET-domain–containing histone methyltransferase that is upregulated in solid cancers, but its expression is hardly detectable in normal tissues. Here, we show that SUV39H2 is highly expressed in ALL cells but not in blood cells from healthy donors and also that SUV39H2 mRNA is expressed at significantly higher levels in bone marrow or blood cells from patients with ALL obtained at diagnosis compared with those obtained at remission (P = .007). In four ALL cell lines (Jurkat and CEM derived from T-ALL and RS4;11 and REH derived from B-ALL), SUV39H2 knockdown resulted in a significant decrease in cell viability (~ 77%, P < .001), likely through induction of apoptosis. On the other hand, SUV39H2 overexpression made cells more resistant to chemotherapy. We conclude that SUV39H2 is a promising therapeutic target and further investigation of this therapeutic approach in ALL is warranted.

Cell context in the control of self-renewal and proliferation regulated by MLL1

Mixed lineage leukemia 1 (MLL1) is a gene that is disrupted by chromosomal translocation characteristically in a large proportion of infant leukemia and also in a fraction of childhood and adult leukemia. MLL1 encodes a chromatin regulatory protein related to the Drosophila Trithorax protein, a well-studied epigenetic factor that functions during development to maintain expression of its target genes. Although tremendous progress has been made understanding the downstream targets of MLL1 fusion oncoproteins and how manipulation of those targets impacts leukemogenesis, very little is known regarding how the initial expression of an MLL1 fusion protein impacts on that cell's behavior, particularly how the cell cycle is affected. Here, we focused on the function of endogenous MLL1 in the stem and progenitor cell types that are likely to be transformed upon MLL1 translocation. Our studies reveal a differential response of stem or progenitor populations to acute loss of MLL1 on proliferation and survival. These data suggest that the effects of MLL1 fusion oncoproteins will initiate the leukemogenic process differentially depending on the differentiation state of the cell type in which the translocation occurs.

T-cell Acute Lymphoblastic Leukemia with del (7) (q11.2q22) and Aberrant Expression of Myeloid Markers

T cell acute lymphoblastic leukemia (ALL) is an invasive disease with a higher incidence in children and adolescents. In terms of Immunophenotype, T-ALL is positive for CD2, CD7, CD34 and HLA-DR, and the level of these markers is increased with increasing age. In addition, the myeloid markers (CD13, CD33) are sometimes expressed in T-ALL. In this study, we introduce a rare case of a 28-year-old woman with T-ALL with aberrant expression of myeloid markers (CD13), without lymphadenopathy and with 94% blasts in bone marrow specimens. The patient has the rare karyotype of 46,XX del(7)(q11.2q22). The presence of del7 is a rare phenomenon in T-ALL.