[History and Perspective of Chemotherapy in Advanced Esophageal Cancer].

Advanced esophageal carcinoma is one of the diseases with a poor prognosis. CF(cisplatin plus 5-FU)therapy and taxanes( paclitaxel or docetaxel)were considered standard treatments for first- and second-line treatment of advanced esophageal carcinoma based on the results of phase Ⅱ trials, although no randomized controlled trials were conducted. Subsequently, anti-epidermal growth factor receptor(EGFR)inhibitors, which had shown efficacy in head and neck cancer and colorectal cancer, were developed but failed to prolong survival both first- and second-line treatment. Immune checkpoint inhibitors have shown efficacy as single agents or in combination with chemotherapy in a variety of cancers, including esophageal cancer, where the KEYNOTE-181 trial and the ATTRACTION-3 trial demonstrated that single-agent pembrolizumab and nivolumab extended survival versus chemotherapy, respectively. In addition, the KEYNOTE-590 trial and the CheckMate 648 trial showed that pembrolizumab plus CF therapy was superior to CF, and nivolumab plus CF therapy and nivolumab plus ipilimumab were superior to CF in advanced esophageal carcinoma. These combinations have become the standard of care for the first-line treatment of advanced esophageal cancer. Immune checkpoint inhibitors had prolonged survival, but the results are still unsatisfactory, and CF therapy combined with immune checkpoint inhibitors and novel agents is being investigated. This article reviews the history of chemotherapy in advanced or recurrent esophageal cancer and discusses future prospects.

Immunotherapy for Unresectable Small Bowel Adenocarcinoma: A Case Series.

BACKGROUND/AIM: The efficacy of systemic therapy for unresectable small bowel adenocarcinoma that is refractory to fluoropyrimidines and oxaliplatin has not yet been established because of the rarity of this cancer. Although immunotherapy with anti-PD-1 antibodies has shown robust efficacy in the treatment of esophagogastric adenocarcinoma, its effectiveness in small bowel adenocarcinoma remains unclear. CASE REPORT: In the first case, a 75-year-old man was diagnosed with metastatic moderately differentiated adenocarcinoma of the jejunum with stable microsatellite instability. After receiving multiple lines of therapy, including fluoropyrimidines plus oxaliplatin, irinotecan, and paclitaxel, the patient was treated with nivolumab and achieved a partial response that lasted for 12 months. In the second case, a 65-year-old man was diagnosed with an unresectable locally advanced duodenal adenocarcinoma. High microsatellite instability was confirmed by polymerase chain reaction-based testing. After showing resistance to 5-fluorouracil and oxaliplatin, the patient received nivolumab and ipilimumab therapy. Although therapy was discontinued because of immune-related colitis and skin rash, a partial response was achieved. CONCLUSION: Treatment with immune checkpoint inhibitors is effective for refractory small bowel adenocarcinoma, irrespective of the microsatellite status.

Treatment with trastuzumab deruxtecan in patients with HER2-positive breast cancer and brain metastases and/or leptomeningeal disease (ROSET-BM).

Therapeutic options for breast cancer patients with brain metastases (BM)/leptomeningeal carcinomatosis (LMC) are limited. Here, we report on the effectiveness and safety of trastuzumab deruxtecan (T-DXd) in human epidermal growth factor receptor 2-positive breast cancer patients with BM. Data were analyzed for 104 patients administered T-DXd. Overall response rate (ORR), progression-free survival (PFS), overall survival (OS), intracranial (IC)-ORR, and IC-PFS were evaluated. ORR by investigator assessment was 55.7% (total population). Median PFS was 16.1 months; 12-month OS rate was 74.9% (total population). Median time-to-treatment failure was 9.7 months. In 51 patients with BM imaging, IC-ORR and median IC-PFS by independent central review were 62.7% and 16.1 months, respectively. In 19 LMC patients, 12-month PFS and OS rates were 60.7% and 87.1%, respectively. T-DXd showed effectiveness regarding IC-ORR, IC-PFS, PFS, and OS in breast cancer patients with BM/active BM, and sustained systemic and central nervous system disease control in LMC patients.Trial Registration: UMIN000044995.

The Impact of Nutritional Support on Survival Outcomes in Patients with Advanced Gastric Adenocarcinoma Treated with Chemotherapy.

Malnutrition and cachexia occur commonly in patients with advanced gastric cancer (AGC). This study elucidated the effect of nutritional support (NS) on survival outcomes among patients with AGC undergoing chemotherapy. We retrospectively evaluated new AGC cases at our institute between January 2015 and January 2021. Inclusion criteria were unresectable or recurrent chemotherapy-treated gastric adenocarcinoma, ECOG performance status (PS) 0-2, and adequate organ function. Time to treatment failure (TTF) and overall survival (OS) were evaluated, and univariate and multivariate analyses identified prognostic factors. A total of 103 eligible patients were separated into groups: 69 patients (67%) into NS and 34 (33%) into routine care (RC). The median follow-up time was 11.0 mo, (0.5-92). NS was offered to patients with poorer PS (p = 0.03), Glasgow prognostic score (GPS) positivity (p = 0.001), and high neutrophil-to-lymphocyte ratios (cut-off ≤ 3, p = 0.02). Median OS and TTF in the RC and NS groups were 11.6 and 10.4 mo, (p = 0.99) and 4.2 and 5.5 mo, (p = 0.07), respectively. Multivariate analyses identified NS (hazard ratio [HR] = 0.53, p = 0.01) and GPS positivity for TTF, and low body mass index (HR = 2.03, p = 0.007) and GPS positivity (HR = 2.25, p = 0.001) for OS as significant prognostic factors. Thus, NS with chemotherapy is a potentially effective intervention for AGC.

Successful Alectinib Treatment for Carcinoma of Unknown Primary with EML4-ALK Fusion Gene: A Case Report.

Gene alteration in anaplastic lymphoma kinase (ALK) is rare, and the efficacy of ALK inhibitors in the treatment of carcinoma of unknown primary (CUP) with ALK alteration remains unclear. The patient was a 56-year-old woman who presented with cervical lymph node swelling. Computed tomography revealed paraaortic, perigastric, and cervical lymph node swelling; ascites; a liver lesion; and a left adrenal mass. A cervical lymph node biopsy was performed, and pathological diagnosis of an undifferentiated malignant tumor was conducted. Finally, the patient was diagnosed with CUP and treated with chemotherapy. To evaluate actionable mutations, we performed a multigene analysis, using a next-generation sequencer (FoundationOne® CDx). It revealed that the tumor harbored an echinoderm microtubule-associated protein-like 4 (EML4) and ALK fusion gene. Additionally, immunohistochemistry confirmed ALK protein expression. Alectinib, a potent ALK inhibitor, was recommended for the patient at a molecular oncology conference at our institution. Accordingly, alectinib (600 mg/day) was administered, and the multiple lesions and symptoms rapidly diminished without apparent toxicity. The administration of alectinib continued for a period of 10 months without disease progression. Thus, ALK-tyrosine kinase inhibitors should be considered in patients with CUP harboring the EML4-ALK fusion gene.

Efficacy of trastuzumab deruxtecan in an advanced gastric cancer patient with brain metastasis.

BACKGROUND: There is no clinical evidence supporting the effectiveness of trastuzumab deruxtecan (T-DXd) for treating advanced gastric cancer (AGC) with brain metastasis. CASE REPORT: This is a case of a 65-year-old man with human epidermal growth factor-2 (HER2)-positive AGC. He was initially treated with capecitabine, cisplatin, and trastuzumab, followed by paclitaxel and ramucirumab, nivolumab, trifluridine and tipiracil, and irinotecan regimens in addition to radiation therapy for brain metastasis. The patient exhibited refractoriness to the standard regimen used for AGC and developed relapse of the brain metastasis after radiation accompanied by headache, nausea, and dizziness. In August 2020, following the approval of T-DXd for HER2-positive AGC, he received T-DXd therapy. After 5 cycles of T-DXd, contrast-enhanced computed tomography and magnetic resonance imaging demonstrated significant tumor shrinkage and improvement of symptoms. CONCLUSION: T-DXd demonstrated effectiveness for the treatment of brain metastasis arising from HER2-positive AGC.

Salvage Chemotherapy by FOLFIRI Regimen for Poorly Differentiated Gastrointestinal Neuroendocrine Carcinoma.

PURPOSE: Chemotherapy is the mainstay treatment for advanced poorly differentiated gastrointestinal neuroendocrine carcinoma (GI-NEC), with platinum-containing regimens being the optimal first-line regimen. However, the role and efficacy of second-line chemotherapy for GI-NEC are unclear. This study aimed to evaluate the feasibility and efficacy of fluorouracil, leucovorin, and irinotecan (FOLFIRI) as second-line therapy in patients with relapsed or recurrent GI-NEC after first-line platinum plus etoposide therapy. METHODS: We retrospectively evaluated eight consecutive patients with unresectable GI-NEC treated between 2017 and 2020. The inclusion criteria were pre-treatment with platinum doublet therapy, performance status (PS) 0-2, having measurable lesions, and treatment with FOLFIRI as second-line therapy. The overall response rate, progression-free survival (PFS), overall survival (OS), safety, and relative dose intensity were evaluated. RESULTS: Five patients met the inclusion criteria. Overall, 37 cycles of FOLFIRI were administered. The relative dose intensities for irinotecan, continuous infusion of 5-FU, and a bolus injection of 5-FU were 76%, 72%, and 54%, respectively. Overall, 2 of the 5 patients achieved partial response (40%), and the duration of response (DOR) was 4.0 months. The PFS and OS rates were 5.8 (95% CI, 1.5-NA) and 11 (95% CI, 6.3-NA) months, respectively. Overall, 4 of the 5 patients (80%) proceeded with further chemotherapy. Grade ≥ 3 adverse events except hematological toxicity included febrile neutropenia (n = 2), anorexia (n = 2), and fatigue (n = 1). Treatment discontinuation due to treatment-related adverse events was not observed. CONCLUSIONS: FOLFIRI showed modest efficacy and feasibility for GI-NEC patients and has thus potential for patients who fail the first-line treatment.

Early phase 2 trial of TAS-205 in patients with Duchenne muscular dystrophy.

OBJECTIVE: Duchenne muscular dystrophy (DMD) is a progressive muscular disease characterized by chronic cycles of inflammatory and necrotic processes. Prostaglandin D2 (PGD2 ) is produced by hematopoietic PGD synthase (HPGDS), which is pathologically implicated in muscle necrosis. This randomized, double-blind, placebo-controlled early phase 2 study (NCT02752048) aimed to assess the efficacy and safety of the novel selective HPGDS inhibitor, TAS-205, with exploratory measures in male DMD patients aged ≥5 years. METHODS: Patients were randomized 1:1:1 to receive low-dose TAS-205 (6.67-13.33 mg/kg/dose), high-dose TAS-205 (13.33-26.67 mg/kg/dose), or placebo. The primary endpoint was the change from baseline in a 6-minute walk distance (6MWD) at Week 24. RESULTS: Thirty-six patients were enrolled, of whom 35 patients were analysed for safety. The mean (standard error) changes from baseline to Week 24 in 6MWD were -17.0 (17.6) m in the placebo group (n = 10), -3.5 (20.3) m in the TAS-205 low-dose group (n = 11), and -7.5 (11.2) m in the TAS-205 high-dose group (n = 11). The mean (95% confidence interval) difference from the placebo group was 13.5 (-43.3 to 70.2) m in the TAS-205 low-dose group and 9.5 (-33.3 to 52.4) m in the TAS-205 high-dose group. No obvious differences were observed in the incidences of adverse events between treatment groups. No adverse drug reactions specific to TAS-205 treatment were observed. INTERPRETATION: The HPGDS inhibitor TAS-205 showed a favorable safety profile in DMD patients. Further research is required to examine the effectiveness of TAS-205 in a larger trial.

Solvent-based paclitaxel or nab-paclitaxel for heavily treated relapsed/refractory small cell lung cancer: Retrospective single-institution observational study.

Treatment options for patients with relapsed/refractory small cell lung cancer (R/R SCLC) are limited, and the efficacy of salvage therapies for heavily treated patients should be assessed. Here, we evaluated the efficacy of paclitaxel (PTX) in R/R SCLC patients.A single-institute retrospective chart review was conducted. The primary endpoint was overall survival (OS), whereas the secondary endpoints were progression-free survival (PFS), overall response rate, disease control rate (DCR), and safety.Thirty-one patients (median age, 69 [range, 56-80] years) were analyzed. The median follow-up period was 122 (range, 28-1121) days. The median OS and PFS were 4.4 and 2.2 months, respectively. Adverse events of grade 3 or higher, other than hematological toxicity, were febrile neutropenia and neuropathy. Multivariate analyses identified the following independent predictors of poor OS: performance status and lactate dehydrogenase at the upper limit of normal.PTX monotherapy showed moderate efficacy with acceptable toxicity in heavily treated patients with R/R SCLC patients.

Primary Mediastinal HER2-positive Apocrine Carcinoma in Mature Teratoma Treated With Anti-HER2 Therapy and Chemoradiation.

BACKGROUND: There are no established guidelines for the management of apocrine carcinomas of the breast; they are treated as a non-specific type of breast cancer. CASE REPORT: We report on the case of a 40-year-old man who developed primary mediastinal apocrine carcinoma overexpressing human epidermal growth factor-2 (HER2). The patient initially underwent complete resection of a mediastinal mature teratoma with a focal apocrine carcinoma component. Two years after surgery, relapse was detected in multiple mediastinal lymph nodes. He received induction chemotherapy including docetaxel, trastuzumab, and pertuzumab; consolidative concurrent chemoradiation was added after six cycles. A complete response was confirmed using computed tomography following this multimodal therapy. After chemoradiation, adjuvant trastuzumab and pertuzumab were administered for 1 year and the patient has since had no evidence of progressive disease. CONCLUSION: A multi-modal regimen that includes an anti-HER2 agent appears to be a promising treatment for patients with HER2-positive extramammary apocrine carcinoma.

Clinical features in very early-onset demyelinating disease with anti-MOG antibody.

BACKGROUND: The clinical features of patients with very early-onset acquired demyelinating syndrome (ADS) with the anti-myelin oligodendrocyte glycoprotein (MOG) antibody are unknown. We investigated the clinical characteristics and described detailed treatment of weekly intramuscular interferon ß-1a (IFNß-1a) in children aged <4years with ADS and the anti-MOG antibody. METHODS: We conducted a retrospective chart review of patients with anti-MOG positivity who were diagnosed as having multiple sclerosis (MS) at <4years of age. RESULTS: Subjects comprised 2 boys and 2 girls. Initial symptoms included ataxia, facial paresis, status epilepticus, and encephalopathy. Abnormal lesions on magnetic resonance imaging scans were often detected in the brainstem and cerebellum as well as the cerebrum. All patients started receiving IFNß-1a at age 3.1-3.5years. The initial doses ranged from 3 to 6µg, which were 1/10-1/5 doses, respectively, for adults. During 0.6-4.3years of IFNß-1a administration, all patients had flu-like symptoms, and 1 patient had an increased liver enzyme level. Although 1 patient discontinued IFNß-1a therapy because of frequent relapses, no patient discontinued therapy due to severe adverse events. CONCLUSIONS: This case series adds novel information regarding the clinical features of children <4years old with ADS and the anti-MOG antibody.

Reconsideration of the diagnosis and treatment of childhood migraine: A practical review of clinical experiences.

OBJECTIVE: To provide insight into the wide spectrum of migraine during childhood to establish practical and comprehensive treatment strategies. BACKGROUND: Although recent studies have confirmed the effect of anti-migraine agents in childhood headaches fulfilling the criteria of migraine without aura, there have been no studies regarding the efficacy of these drugs in childhood migraine without aura not filling the diagnostic criteria. METHODS: In total, 154 patients with a clinical diagnosis of migraine, with onset of repetitive headaches at the age of ⩽15years, were retrospectively included from clinics in seven tertiary medical centers. RESULTS: Patients' diagnoses included migraine with aura (n=49), migraine without aura (n=65), clinical migraine without aura not fulfilling International Classification of Headache Disorders-3 beta criteria (suspected migraine without aura; n=38), and hemiplegic migraine (n=2). Abortive medicine was effective in 74 of 97 patients, and preventive medicine was effective in 61 of 84 patients. Drugs with high efficacy were acetaminophen and ibuprofen for abortive therapy and cyproheptadine, amitriptyline, and propranolol for preventive therapy. Psychosocial problems were less common, and abnormalities on electroencephalography were more common in the suspected migraine without aura group. Otherwise, clinical features and drug responsibility were comparable among the migraine with aura, migraine without aura, and suspected migraine without aura groups. Retrospectively, experts clinically diagnosed childhood migraine without aura when the headache met at least one of the three criteria B, C, and D in International Classification of Headache Disorders-3 beta in addition to A and E. Abortive and preventive medication including paroxetine (n=2) benefited 10 and 15 of the 33 patients with daily headache, respectively. Psychotherapy/counseling (n=4), treatment for orthostatic dysregulation (n=4), and elimination of stressors (n=3) markedly alleviated headache in this group. CONCLUSION: Our results indicated that those with suspected migraine without aura not filling International Classification of Headache Disorders diagnostic criteria should be included in the treatment for migraine. Treatment should also be targeted to comorbid developmental disorders, orthostatic dysregulation, and psychosocial problems in patients with refractory daily headaches.

Anti-myelin oligodendrocyte glycoprotein (MOG) antibodies in a Japanese boy with recurrent optic neuritis.

BACKGROUND: Myelin oligodendrocyte glycoprotein (MOG) localizes on the outermost surface of the myelin sheath and oligodendrocytes in the central nervous system (CNS). Autoantibodies against MOG are reportedly found in patients with spectrum of inflammatory demyelinating diseases of the CNS, including acute disseminated encephalomyelitis, multiple sclerosis, and neuromyelitis optica. In addition, recent studies have emphasized an association between anti-MOG antibodies and optic neuritis. PATIENT: We present the first case report of a 7-year-old Japanese boy who was positive for anti-MOG antibodies. He experienced four episodes of unilateral optic neuritis and one seizure event. Magnetic resonance imaging revealed T2-hyperintense lesions in the subcortical white matter and midbrain. Although he fulfilled the diagnostic criteria for multiple sclerosis, recombinant interferon beta did not prevent recurrence. Established cell-based immunoassays revealed that he was positive for anti-MOG antibodies and negative for anti-aquaporin 4 antibodies. CONCLUSIONS: Our case report supports the relationship between anti-MOG antibodies and recurrent optic neuritis. Additional studies are needed to establish the clinical significance of anti-MOG antibodies for diagnosis, treatment, and prognosis.

Utility of real-time three-dimensional echocardiography for Duchenne muscular dystrophy with echocardiographic limitations.

Duchenne muscular dystrophy (DMD) is strongly associated with a unique form of dilated cardiomyopathy. Cardiac complications are the leading cause of death in DMD; thus, longitudinal assessments and early intervention for cardiac dysfunction are necessary to improve prognosis. Two-dimensional echocardiography, which is routinely used for cardiac assessment, has some limitations for quantitative analyses in DMD patients with thoracic deformities and regional wall motion abnormalities in the left ventricle. Recently, real-time three-dimensional echocardiography has emerged as a feasible tool for cardiac assessment in various cardiac diseases. The aim of this study was to examine the utility of this technology in DMD. We evaluated left ventricular ejection fraction (LVEF), a major parameter of left ventricular function, in 17 male DMD patients. LVEF values measured by real-time three-dimensional echocardiography were compared with those determined by two established nuclear cardiology methods: "the first-pass method of radionuclide angiocardiography" and "quantitative electrocardiogram-gated single-photon emission computed tomography". A good correlation was observed for LVEF values, particularly between real-time three-dimensional echocardiography and "the first-pass method of radionuclide angiocardiography" (r=0.90, p<0.05). Thus, real-time three-dimensional echocardiography can provide an accurate measurement of LVEF in DMD patients with echocardiographic limitations.

Mutations in the C-terminal domain of ColQ in endplate acetylcholinesterase deficiency compromise ColQ-MuSK interaction.

Acetylcholinesterase (AChE) at the neuromuscular junction (NMJ) is mostly composed of an asymmetric form in which three tetramers of catalytic AChE subunits are linked to a triple helical collagen Q (ColQ). Mutations in COLQ cause endplate AChE deficiency. We report three patients with endplate AChE deficiency with five recessive COLQ mutations. Sedimentation profiles showed that p.Val322Asp and p.Arg227X, but not p.Cys444Tyr, p.Asp447His, or p.Arg452Cys, inhibit formation of triple helical ColQ. In vitro overlay of mutant ColQ-tailed AChE on muscle sections of Colq(-/-) mice revealed that p.Cys444Tyr, p.Asp447His, and p.Arg452Cys in the C-terminal domain (CTD) abrogate anchoring ColQ-tailed AChE to the NMJ. In vitro plate-binding assay similarly demonstrated that the three mutants inhibit binding of ColQ-tailed AChE to MuSK. We also confirmed the pathogenicity of p.Asp447His by treating Colq(-/-) mice with adeno-associated virus serotype 8 carrying mutant COLQ-p.Asp447His. The treated mice showed no improvement in motor functions and no anchoring of ColQ-tailed AChE at the NMJ. Electroporation of mutant COLQ harboring p.Cys444Tyr, p.Asp447His, and p.Arg452Cys into anterior tibial muscles of Colq(-/-) mice similarly failed to anchor ColQ-tailed AChE at the NMJ. We proved that the missense mutations in ColQ-CTD cause endplate AChE deficiency by compromising ColQ-MuSK interaction at the NMJ.

[Clinical features of congenital myasthenic syndrome in Japan].

OBJECTIVE: We examined the clinical and neurophysiological features of Japanese patients with congenital myasthenic syndrome (CMS). METHOD: Subjects were five patients who were diagnosed with CMS on the basis of clinical course, repetitive nerve stimulation (RNS), and genetic analysis. RESULTS: Four patients manifested motor retardation within one year of birth, while one manifested motor intolerance at three years of age. The most characteristic symptom observed in all the patients was fluctuating muscle weakness, which varied on a daily basis or continued for several days after the late infancy period. Only one patient manifested daily fluctuation of muscle weakness. RNS of the accessory nerve evoked a decrementing response in three patients who were examined;however, RNS of the median, ulnar, and tibial nerves (one patient each) did not evoke such responses. After the edrophonium chloride test, no improvement was seen even if the patients manifested ptosis. For judgment of this test, improvement in decrementing rate observed while performing RNS was useful. All five patients who were administered medication based on the results of genetic analysis demonstrated an improvement in their symptoms. CONCLUSION: We suggest that CMS can be diagnosed based on careful examination and electrophysiological results. CMS is a treatable disorder, and therefore, correct diagnosis is important.

[Anti-NMDA receptor antibody encephalitis with recurrent optic neuritis and epilepsy].

A previously healthy, 10-year-old girl developed left optic neuritis that treated with oral prednisolon (PSL). During the following 8 months, the patient exhibited right optic neuritis 3 days after discontinuation of PSL therapy and three episodes of epileptic seizures 3 weeks after PSL withdrawal Cerebrospinal fluid (CSF) examination revealed pleocytosis (mononuclear cells), increased IgG index, and positive oligoclonal IgG expression. Brain MRI showed multiple cortical, subcortical, and leptomeningeal enhanced lesions. However, spinal cord MRI revealed no lesions. Neither autoantibodies to nuclear, thyroid, alpha-enolase, glutamic acid decarboxylase, nor aquaporin 4 was detected. However, anti-NMDA receptor antibodies (NMDAR-Ab) were present in her CSF. This patient is the second reported case of NMDAR-related encephalitis with recurrent optic neuritis. The possibility of seronegative neuromyelitis optica (NMO) could not be ruled out for the symptom of recurrent optic neuritis. However, the presence of NMDAR-Ab in the CSF together with increased IgG index and oligoclonal IgG bands, which are usually negative in NMO suggested that this patient is NMDAR-related encephalitis combined with rare symptom of optic neuritis for this type of encephalitis, though we need to wait larger number of patients' accumulation to conclude that the optic neuritis could be one of the features of NMDAR-related encephalitis.

Loss of Borealin/DasraB leads to defective cell proliferation, p53 accumulation and early embryonic lethality.

Borealin/DasraB is a member of the chromosomal passenger protein complex (CPC) required for proper segregation of chromosomes during mitosis. In Drosophila melanogaster, inactivation of Borealin/DasraB results in polyploidy, delayed mitosis and abnormal tissue development, indicating its critical role for cell proliferation. However, the in vivo role of mammalian Borealin/DasraB remains unclear. Here, we analyzed the expression of Borealin/DasraB and found that borealin is widely expressed in embryonic tissues and later restricted to adult tissues which relies on rapid cell proliferation. To determine the role of borealin during mouse development, we generated borealin-null mice through targeted disruption. While heterozygous mice developed normally, disruption of both borealin alleles resulted in early embryonic lethality by 5.5 dpc (days postcoitus) due to mitotic defects and apoptosis in blastocyst cells that showed microtubule disorganization and no CPC enrichment. At 5.5 dpc, borealin-null embryos exhibited excessive apoptosis and elevated expression of p53. However, loss of p53 did not abrogate or delay embryonic lethality, revealing that Borealin/DasraB inactivation triggered impaired mitosis and apoptosis though p53-independent mechanisms. Our data show that Borealin/DasraB is essential for cell proliferation during early embryonic development, and its early embryonic lethality cannot be rescued by the loss of p53.