Page 192 - 2022_01-Haematologica-web

A. Hecht et al.
(Figure 4).1,5,12,23 Thirty-one of the 33 CBL-mutated patients were classified as having low methylation irrespective of whether their mutation was germline or somatic in nature, while the other two patients, one with a germline muta- tion, the other with a somatic mutation, were classified as having intermediate methylation. Notably, both patients who were classified as having intermediate methylation relapsed after HSCT. Unsupervised hierarchical clustering did not reveal any differences in methylation patterns among patients with germline CBL mutations who experi- enced spontaneous remission, survived more than 4 years without HSCT or died without receiving treatment.
To demonstrate the wide spectrum of clinical presenta- tions and the variability in treatment decisions we share the following vignettes.
Vignette 1: UPN2903
A previously healthy 12-month-old female infant was noted to have thrombocytopenia with a normal hemoglobin concentration and white blood cell count on a routine full blood count. The patient was asymptomatic and was observed. At 3 years of age, leukoerythroblastosis was noted on her peripheral blood smear, and her fetal hemoglobin concentration was noted to be elevated for age. Her bone marrow was normocellular for age with trilin- eage hematopoiesis and no dysplasia. Genetic sequencing revealed a CBL p.Y371H mutation at 70% VAF. The patient was noted to have possible facial dysmorphology. A presumptive diagnosis of germline CBL-associated JMML was made, although no germline testing was performed at that time. The patient was observed for nearly 2 years at which point her white cell count increased to 40x109/L. A repeat bone marrow exami- nation was performed, which revealed transformation to acute myeloid leukemia with 20% blasts and a der(16)t(1;16) on cytogenetics resulting in partial deletion of 16q and partial tri- somy for 1q. Repeat tumor testing revealed that the CBL muta- tion had decreased to 52% VAF, and additional NRAS p.G13D (22%) and KRAS p.T58I (3%) mutations were noted. The patient went on to receive various chemotherapeutic regimens, including daunorubicin, cytarabine and etoposide, mitoxantrone and cytarabine, 6-mercaptopurine, hydroxyurea, trametinib and sorafenib, but was never able to achieve remission. The patient was transplanted with 10% bone marrow blasts using busulfan, cyclophosphamide, and melphalan conditioning, but died of infection and graft-versus-host disease shortly after the trans- plant. Post-mortem, a cord blood sample was analyzed and con- firmed the absence of a germline CBL mutation. However, a het- erozygous RUNX1 p.R166Q mutation was detected in the cord blood, indicating that the patient had an autosomal dominant familial platelet disorder with propensity to myeloid malignancy syndrome.
Vignette 2: UPN2056
A 6-month-old patient with several congenital anomalies including hypoplastic kidneys, midgut malrotation, webbed neck, and choanal atresia was suspected of having Kabuki or Noonan syndrome. Over time, he displayed significant develop- mental delay and short stature. At 3 years of age, this patient developed a myeloproliferative disorder with features suggestive of JMML, including monocytosis, anemia, and juvenile xan- thogranulomas, and fewer than 5% blasts in his bone marrow. At this time, tumor sequencing revealed a novel homozygous frameshift mutation in exon 7 of CBL. Germline testing revealed the identical heterozygous deletion. Of note, the patient had an identical twin brother who developed a myeloproliferative disor- der at nearly the same time with similar congenital anomalies
and was found to carry the same mutation. The patient had a splenectomy at age 4 years, but his monocytosis persisted. The patient had multiple medical comorbidities, including chronic renal disease, seizures and hypothyroidism, and died of compli- cations unrelated to JMML.
Vignette 3: UPN2977
A previously healthy 9-month-old female was evaluated for fatigue and splenomegaly. A full blood count revealed a white blood count of 52x109/L, hemoglobin concentration of 9.0 g/dL, and platelet count of 68x109/L. Bone marrow evaluation demon- strated monocytosis with normal cytogenetics. Genetic testing revealed a germline heterozygous CBL p.Y371H mutation with loss of heterozygosity in the bone marrow. She was initially observed, but subsequently failed to thrive and developed wors- ening splenomegaly and leukocytosis (peak WBC of 121x109/L). She was started on 6-mercaptopurine with a tran- sient improvement in her white blood cell count. She experienced recurrent splenomegaly, leukocytosis, and thrombocytopenia, so went on to receive two cycles of fludarabine/cytarabine and underwent splenectomy. Despite these interventions, she had persistent leukocytosis. Repeat bone marrow evaluation was consistent with persistent JMML by morphology, but demon- strated new cytogenetic changes with a 3q deletion. Given her refractory JMML and cytogenetic evolution, she received four cycles of azacitidine followed by a haplo-identical peripheral blood stem cell transplant from her mother with busulfan, cyclophosphamide, and melphalan conditioning. She had engraftment failure, so received a stem cell boost and then ulti- mately received 5/6 unrelated umbilical cord blood transplant with fludarabine, cyclophosphamide, and total body irradiation as conditioning. Her post-transplant course was complicated by recurrent bacteremia and cytomegalovirus viremia. She is now in clinical remission more than 1 year after transplantation and is doing well.
Discussion
In this study, we comprehensively analyzed the largest cohort of CBL-mutated JMML patients described to date. The clinical courses and outcomes of the 33 patients ana- lyzed varied dramatically, and a typical “watch and wait” approach was not appropriate for all patients.
Interestingly, we found that five of the 33 patients had somatically acquired CBL mutations. To our knowledge, this is the first time somatic CBL mutations have been described in JMML. All mutations, whether germline or somatic in nature, were located at the known hotspot loci in the CBL gene. No secondary mutations were found in any other JMML-associated genes in any of these patients at diagnosis. Moreover, patients with germline or somatic CBL mutations did not differ in their clinical presentation or laboratory features at diagnosis. Surprisingly, the over- all survival rate of patients with germline CBL mutations in our cohort was lower than that in previous reports. One question that remains unanswered is whether trans- plantation for germline CBL-mutant patients can effec- tively decrease or prevent the known non-hematologic complications of CBL-syndrome and potentially increase overall survival. There was a trend towards improved overall survival in patients with germline mutations who underwent HSCT but transplant-related mortality remains a concern.
In a prior study, five of six patients with CBL-syndrome
184
haematologica | 2022; 107(1)