Transient EDTA-dependent pseudothrombocytopenia and ulcerative colitis recurrence during chemotherapy: A case of misleading platelet count results attributable to a laboratory artifact.

Key Clinical Message: EDTA-dependent pseudothrombocytopenia as well as myelosuppression should be suspected when thrombocytopenia occurs in patients with autoimmune disease during chemotherapy. Abstract: A patient with pancreatic cancer and ulcerative colitis developed transient ethylenediaminetetraacetic acid (EDTA)-dependent pseudothrombocytopenia with exacerbation of ulcerative colitis during chemotherapy. Unfortunately, pseudothrombocytopenia could not be immediately detected because thrombocytopenia was masked by a reasonable time course of adverse events associated with chemotherapy and ulcerative colitis recurrence. When thrombocytopenia occurs during chemotherapy, especially in patients with autoimmune diseases, EDTA-dependent pseudothrombocytopenia and bone marrow suppression caused by anti-cancer agents should be suspected.

Multicenter phase II study of capecitabine plus oxaliplatin in older patients with advanced gastric cancer: the Tokyo Cooperative Oncology Group (TCOG) GI-1601 study.

BACKGROUND: Capecitabine plus oxaliplatin (CapeOX) is a standard treatment option for advanced gastric cancer (AGC). We conducted a prospective multicenter phase II study to evaluate the efficacy and safety of CapeOX as a first-line therapy for AGC in older patients. METHODS: Chemotherapy-naive patients aged ≥ 70 years with AGC were eligible. Initial treatment comprised capecitabine (2000 mg/m2 on days 1-14) and oxaliplatin (130 mg/m2 on day 1) every 3 weeks. After the initial feasibility assessment, the dose was reduced considering toxicity (capecitabine, 1500 mg/m2 on days 1-14; and oxaliplatin, 100 mg/m2 on day 1 every 3 weeks). The primary endpoint was overall survival (OS). RESULTS: In total, 108 patients were enrolled, of whom 104 were evaluated. Thirty-nine patients received the original-dose treatment, whereas 65 received the reduced-dose treatment. The median OS, progression-free survival (PFS), and time to treatment failure (TTF) were 12.9 (95% CI 11.6-14.8), 5.7 (95% CI 5.0-7.0), and 4.3 (95% CI 3.9-5.7) months, respectively, for all patients; 13.4 (95% CI 9.5-16.0), 5.8 (95% CI 4.1-7.8), and 5.3 (95% CI 3.5-7.2) months in the original-dose group; and 12.8 (95% CI 11.3-15.3), 5.7 (95% CI 4.4-7.0), and 4.1 (95% CI 3.7-5.7) months in the reduced-dose group. The most common grade 3/4 toxicities were neutropenia (17.9%), anemia (12.8%), and thrombocytopenia (12.8%) in the original-dose group and neutropenia (13.8%) and anorexia (12.3%) in the reduced-dose group. CONCLUSIONS: These findings demonstrate CapeOX's efficacy and safety in older AGC patients.

A polymorphism in ABCA2 is associated with neutropenia induced by capecitabine in Japanese patients with colorectal cancer.

PURPOSE: Capecitabine is a prodrug that converts to 5-fluorouracil (5-FU) in three steps. A previous study showed that ABCA2 rs2271862 (C > T) and ABCG5 rs6720173 were associated with increased clearance of 5-FU and 5'-deoxy-5-fluorouridine, respectively, in Spanish patients with colorectal cancer (CRC) (Br J Clin Pharmacol 2021) and reported that ABCA2 rs2271862 was associated with decreased risk of capecitabine-induced neutropenia. Other studies have reported that ABCB1 rs1128503, rs2032592, and rs1045642 were associated with capecitabine-induced toxicity in Spanish CRC patients (Oncotarget 2015, Phamacogenomics 2010). Here, we prospectively examined the effects of ABC transporter genes polymorphisms on capecitabine pharmacokinetics and toxicity. METHODS: We enrolled patients with postoperative CRC treated with adjuvant capecitabine plus oxaliplatin (CapeOX) and patients with metastatic CRC receiving CapeOX. Pharmacokinetic analysis of the first capecitabine dose (1000 mg/m2) was performed on day 1. We analyzed plasma concentrations of capecitabine and its three metabolites by high-performance liquid chromatography and ABC transporter genes polymorphisms using direct sequencing. RESULTS: Patients with ABCA2 rs2271862 T/T genotype had significantly lower area under the plasma concentration-time curve of capecitabine, but not of its metabolites, which were divided by the dose of the parent drug, than patients with C/C or C/T genotype (P = 0.0238). Frequency of ≥ grade 2 neutropenia was significantly lower in patients with ABCA2 rs2271862 T/T genotype (P = 0.00915). Polymorphisms in ABCG5 and ABCB1 were not associated with capecitabine pharmacokinetics and toxicity. CONCLUSIONS: We found that ABCA2 polymorphism was significantly associated with systemic exposure to capecitabine and capecitabine-induced neutropenia in Japanese patients with CRC.

TP53 Gain-of-Function Mutation is a Poor Prognostic Factor in High-Methylated Metastatic Colorectal Cancer.

BACKGROUND: Neither TP53 mutation nor DNA methylation status has been established as a biomarker alone of metastatic colorectal cancer. We analyzed the association between TP53 mutation functional subtypes and genome-wide DNA methylation status (GWMS) as combined prognostic markers. METHODS: Patient clinical data were obtained from the TRICOLORE study, a randomized phase III trial. The TP53 mutations were classified into wild-type, gain-of-function (GOF) mutations, and non-gain-of-function (non-GOF) mutations. GWMS of the tumor tissues classified them into high-methylated colorectal cancer (HMCC) and low-methylated colorectal cancer (LMCC). Overall survival (OS) was compared based on these subgroups. RESULTS: Of the 209 patients, 60 (28.7%) were HMCC and 149 (71.3%) were LMCC, 35 (16.7%) were TP53 wild-type and 174 (83.3%) were TP53 mutants including 79 (45.4%) GOF mutations and 95 (54.6%) non-GOF mutations. The OS of the HMCC group was shorter than that of the LMCC group (median 25.3 vs. 40.3 months, P < .001, hazard ratio 1.87) in the total cohort. The combined subgroup analyses of GWMS and TP53 mutation subtypes showed that the HMCC/GOF group had significantly shorter OS than the HMCC/non-GOF group, the LMCC/GOF group, and the LMCC/non-GOF group (median 17.7; 35.3, 40.3, and 41.2 months, P = .007, P < .001, and P < .001, respectively), regardless of the primary tumor location. By the multivariate analysis, only HMCC (P = .009) was a poor prognostic factor in the GOF mutation group. CONCLUSIONS: TP53 GOF with HMCC is a newly identified poorest prognostic molecular subset in metastatic colorectal cancer.

Dexamethasone to prednisolone rotation relieved hiccups in colorectal cancer patient continuing teleworking during anticancer therapy.

We present a case of chemotherapy-induced hiccups that were alleviated by steroid rotation. Hiccups are often overlooked, but they have an impact on the patient's quality of life. In the COVID-19 era, web-based teleworking has become an important tool, hiccups during a teleconference should be noted as a concern for patients.

Pancreatic hamartoma: Possibility of a preoperative diagnosis via endoscopic ultrasound-guided fine-needle aspiration biopsy.

Endoscopic ultrasound-guided fine-needle aspiration biopsy (EUS-FNAB) is useful for preoperatively diagnosing various pancreatic tumors. Although there is a risk of complications, such as pancreatitis, this procedure achieves the crucial need of reducing unnecessary invasive surgery for benign lesions. Herein, we reported a surgically resected case of pancreatic hamartoma in the pancreatic head whose retrospective analysis revealed that the specimens obtained via EUS-FNAB contained hamartoma fragments. Pancreatic hamartoma is an extremely rare benign disease that is exceptionally difficult to diagnose before surgical resection owing to its rarity and lack of established imaging findings. To the best of our knowledge, the preoperative diagnosis of pancreatic hamartoma via EUS-FNAB specimens has not been reported to date. Herein, postoperative EUS-FNAB evaluation revealed a collection of pancreatic hamartoma lesions, although the initial diagnosis was pancreatic tissue with focal atrophy and fibrosis. Diagnosis using EUS-FNAB can be challenging owing to the very small sample size. If mature acini and ducts with fibrous stroma without islets are observed in the EUS-FNAB specimen, pancreatic hamartoma should be considered as a differential diagnosis. Thus, careful follow-up or reexamination of EUS-FNAB should be considered instead of surgery if a benign lesion is suspected preoperatively.

Phase II Study of S-1 and Irinotecan Plus Bevacizumab as Second-line Treatment for Patients With Metastatic Colorectal Cancer Resistant to the Fluoropyrimidine-oxaliplatin-cetuximab Regimen.

BACKGROUND/AIM: The usefulness of angiogenesis inhibitors as second-line treatment after the progression of anti-epidermal growth factor receptor antibody drug-containing regimens for RAS wild-type metastatic colorectal cancer (mCRC) has not been fully investigated. Therefore, we conducted a phase II study to verify the efficacy and safety of the combination of S-1 and irinotecan plus bevacizumab (SIRB regimen) as second-line treatment for patients with oxaliplatin and cetuximab-refractory KRAS wild-type mCRC. PATIENTS AND METHODS: Patients with mCRC who had previously received oxaliplatin and cetuximab-containing regimen were eligible for this study. Patients were infused with bevacizumab 7.5 mg/kg and irinotecan 150 mg/m2 intravenously on day 1, whereas S-1 80 mg/m2 was administered orally twice daily until day 15, followed by a 7-day drug holiday period. The primary end point was 6-month progression-free survival (PFS) rate. RESULTS: In total, 17 patients were enrolled in this study. The 6-month PFS rate was 64.7% [95% confidence interval (CI)=41.99-87.43], median PFS was 10.1 months (95%CI=4.11-17.28), and median overall survival was 21.8 months (95%CI=9.79-37.91). The response rate was 23.5% (95%CI=6.81-49.90%). Grade ≥3 adverse events were observed in 10% of patients, and included leukopenia [3 (17.6%)], neutropenia [5 (29.4%)], anorexia [2 (11.8%)], diarrhea [2 (11.8%)], and hypertension [3 (17.6%)]. No treatment-related deaths or febrile neutropenia were observed. CONCLUSION: The SIRB regimen might be a promising second-line treatment option for patients with oxaliplatin and cetuximab-refractory KRAS wild-type mCRC in terms of efficacy and safety.

Clinical features and mechanism of liver injury in patients with mild or moderate coronavirus disease 2019.

BACKGROUND AND AIM: We aimed to identify clinical features that suggest that coronavirus disease 2019 (COVID-19) should be a differential diagnosis in patients presenting with a chief complaint of fever and abnormal liver function. METHODS: We retrospectively studied the presence or absence of abnormal liver function in 216 patients diagnosed with mild-moderate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection between February and September 2020. RESULTS: Abnormal liver function was observed in 51 patients with mild-moderate COVID-19. The median peak aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH) levels were 57.5, 75.5, and 332.5 U/L, respectively. The median number of days from symptom onset to peak AST, ALT, and LDH were 8.5, 9, and 8.5, respectively. The median peak LDH/AST ratio was 9.0. Low lymphocyte-to-white blood cell ratio and elevated LDH were found to be independent contributing factors for intensive care unit (ICU) admission on a multivariate analysis. CONCLUSIONS: AST-predominant AST/ALT/LDH elevation peaking 8-9 days after symptom onset and not accompanied by elevated alkaline phosphatase or gamma-glutamyl transferase may be a useful clinical feature for differentiating COVID-19 from other diseases. Since the median LDH/AST ratio was 9.0, it seems that the abnormal liver function caused by SARS-CoV-2 is an indirect damage to liver cells due to elevated cytokine levels caused by liver-infiltrating lymphocytes. SARS-CoV-2 infection should be considered in patients presenting with a chief complaint of fever and liver injury; those with a high lymphocyte-to-white blood cell ratio or and a high LDH/AST ratio may be admitted to the ICU.

Combination therapy of bevacizumab with either S-1 and irinotecan or mFOLFOX6/CapeOX as first-line treatment of metastatic colorectal cancer (TRICOLORE): Exploratory analysis of RAS status and primary tumour location in a randomised, open-label, phase III, non-inferiority trial.

AIM: The TRICOLORE trial previously demonstrated that S-1 and irinotecan plus bevacizumab was non-inferior, based on progression-free survival (PFS), to 5-fluorouracil, leucovorin and oxaliplatin (mFOLFOX6)/capecitabine and oxaliplatin (CapeOX) plus bevacizumab as first-line chemotherapy for metastatic colorectal cancer (mCRC). Overall survival (OS) data were immature at the time of the primary analysis. METHODS: In total, 487 patients from 53 institutions with previously untreated mCRC were randomly assigned (1:1) to receive either mFOLFOX6/CapeOX plus bevacizumab (control group) or S-1 and irinotecan plus bevacizumab (experimental group; 3- or 4-week regimen). The final OS data were analysed from follow-up data collected until 30th September 2017. RESULTS: With a median follow-up period of 48.7 months, median survival times were 32.6 and 34.3 months (hazard ratio [HR]: 0.89, 95% confidence interval [CI]: 0.72-1.10, P = 0.293) and median PFS durations were 10.8 and 14.0 months in the control and experimental groups, respectively (HR: 0.86, 95% CI: 0.71-1.04, P < 0.0001 for non-inferiority). In patients with left-sided RAS wild-type tumours, median PFS durations were 11.4 and 16.9 months in the control and experimental groups, respectively (HR: 0.68, 95% CI: 0.48-0.96, P = 0.028). CONCLUSION: S-1 and irinotecan plus bevacizumab resulted in comparable OS and non-inferior PFS with that of mFOLFOX6/CapeOX plus bevacizumab treatment as first-line chemotherapy for patients with mCRC. We recommend the use of S-1 and irinotecan plus bevacizumab as a standard first-line regimen independent of tumour sidedness or RAS status in mCRC. TRIAL REGISTRATION: UMIN-CTR: 000007834.

Advanced colorectal cancer subtypes (aCRCS) help select oxaliplatin-based or irinotecan-based therapy for colorectal cancer.

Oxaliplatin (OX) and irinotecan (IRI) are used as key drugs for the first-line treatment of metastatic colorectal cancer (mCRC). However, no biomarkers have been identified to decide which of the drugs is initially used. In this translational research (TR) of the TRICOLORE trial, the advanced colorectal cancer subtype (aCRCS) was analyzed as a potential biomarker for the selection of OX or IRI. We collected 335 (68.8%) formalin-fixed, paraffin-embedded (FFPE) primary tumor specimens from 487 patients registered in the TRICOLORE trial and performed direct sequencing and immunohistochemical staining of CRC-related genes, comprehensive gene-expression analysis, and genome-wide methylation analysis. The progression-free survival (PFS) of the IRI group was significantly better compared with the OX group in BRAF wild-type (WT), PTEN-positive, and aCRCS A1 patients. Among the molecular factors, aCRCS were only associated with the PFS of OX and IRI groups. The PFS of the IRI group was significantly better compared with the OX group in aCRCS A1 + B1 (hazard ratio [HR] = 0.58; 95% confidence interval [CI] = 0.41-0.82; P = .0023). In contrast, the OX group had better PFS compared with the IRI group in aCRCS B2, although this was not statistically significant (HR = 1.66; 95% CI = 0.94-2.96; P = .083). Nearly half of patients with mCRC (46.8%, aCRCS A1 + B1) respond well to IRI, while only about 18.5% (aCRCS B2) of patients with mCRC responded well to OX. In conclusion, the aCRCS might be a predictive factor for the clinical outcomes of OX-based and IRI-based therapies.

Effect of early tumor response on the health-related quality of life among patients on second-line chemotherapy for advanced gastric cancer in the ABSOLUTE trial.

BACKGROUND: This study evaluated the association between early tumor response at 8 weeks, previously reported as a positive outcome prognosticator, and health-related quality of life (HRQOL) in advanced gastric cancer (AGC) patients enrolled in the ABSOLUTE trial. METHODS: HRQOL was assessed using the EuroQol-5 Dimension (EQ-5D) utility index score in patients with complete response (CR) + partial response (PR) and progressive disease (PD) at 8 weeks, and time-to-deterioration (TtD) of the EQ-5D score, with the preset minimally important difference (MID) of 0.05, was compared between these populations. Among the enrolled patients, 143 and 160 patients were assessable in weekly solvent-based paclitaxel (Sb-PTX) arm and weekly nanoparticle albumin-bound paclitaxel (nab-PTX) arm, respectively. RESULTS: Changes of the EQ-5D score from baseline to 8 weeks in the nab-PTX arm were 0.0009 and - 0.1229 in CR + PR and PD patients, respectively; the corresponding values for the Sb-PTX arm were - 0.0019 and - 0.1549. For both treatments, changes of the EQ-5D score from baseline at 8 weeks were significantly larger in patients with PD than in those with CR + PR. The median TtD was 3.9 and 2.2 months in patients with CR + PR and PD, respectively, for nab-PTX [hazard ratio (HR) = 0.595, 95% confidence interval (CI) 0.358-0.989]. For Sb-PTX, the corresponding values were 4.7 and 2.0 months (HR = 0.494, 95% CI 0.291-0.841). CONCLUSIONS: Early tumor shrinkage was associated with maintained HRQOL in AGC patients on the second-line chemotherapy with taxanes.

A case of recurrent malignant phyllodes tumor undergoing nipple-sparing mastectomy with immediate breast reconstruction.

BACKGROUND: Although the primary treatment for malignant phyllodes tumor (PT) is complete surgical excision with either breast-conserving surgery or total mastectomy, recent technical advances have led to the adoption of nipple-sparing mastectomy (NSM) with immediate breast reconstruction (IBR). CASE PRESENTATION: A 28-year-old woman noticed a mass in her left breast that was rapidly increasing in size. She underwent tumor excision and a histological diagnosis of marked degenerative and necrotic induration suggested benign PT. One year later, however, she was found to have recurrent masses in the left breast on follow-up mammography and sonography. Needle biopsy was performed and the tumor was diagnosed as borderline or malignant PT. She underwent NSM and sentinel lymph-node biopsy with IBR using a tissue expander. Histological examination of the mastectomy specimen showed multiple fibroepithelial tumors with marked stromal overgrowth, focal necrosis, and hemorrhage. Stromal cells showed pleomorphism and a maximal mitotic rate of approximately 25 per 10 high-power fields. The tumor was diagnosed as malignant PT. She did not receive adjuvant chemotherapy or radiation treatment. At 3-year follow-up, the patient remains free of disease and highly satisfied with the cosmetic results. CONCLUSIONS: NSM with IBR is not a contraindication for malignant PT. It is both curative and can offer an appealing cosmetic option for localized malignant PT.

Phase 2 study of irinotecan plus cetuximab rechallenge as third-line treatment in KRAS wild-type metastatic colorectal cancer: JACCRO CC-08.

BACKGROUND: Regorafenib or trifluridine/tipiracil as third-line treatment have limited efficacy in metastatic colorectal cancer (mCRC). METHODS: This Phase 2 trial evaluated the efficacy and safety of irinotecan plus cetuximab rechallenge as third-line treatment in KRAS wild-type mCRC patients who achieved clinical benefit with first-line cetuximab-containing therapy. The primary endpoint was 3-month progression-free survival (PFS) rate. A sample size was calculated; 30 patients with a 3-month PFS rate of 45% deemed promising and 15% unacceptable. Patients with greater and less than the cut-off value of cetuximab-free intervals (CFIs) were classified into the long and short CFI groups, respectively, in subgroup analyses. RESULTS: Among 34 eligible patients who received treatment at least once, 3-month PFS rate was 44.1% (95% confidence interval, 27.4-60.8%). The median PFS and overall survival (OS) were 2.4 and 8.2 months, respectively. The response and disease control rates were 2.9 and 55.9%, respectively. PFS and OS were significantly longer in the long- than in the short CFI group. CONCLUSIONS: Irinotecan plus cetuximab rechallenge as third-line treatment for KRAS wild-type mCRC was safe and had promising activity, especially in those with a long CFI, warranting further investigation in a Phase 3 randomised trial. CLINICAL TRIAL REGISTRATION: UMIN000010638.

Expression of clock gene Dbp in omental and mesenteric adipose tissue in patients with type 2 diabetes.

INTRODUCTION: We previously reported in ob/ob mice, one of animal models of human type 2 diabetes mellitus (DM2), that (i) acetylation of histone H3 lysine 9 (H3K9) at the promoter region of clock gene Dbp and DBP mRNA expression are reduced in epididymal adipose tissue, (ii) binding of DBP to the promoter region of peroxisome proliferator-activated receptor (Ppar)-γ and mRNA expression of PPAR-γ1sv were decreased in preadipocytes and (iii) adiponectin secretion was decreased, leading to the impaired insulin sensitivity. RESEARCH DESIGN AND METHODS: The present study was undertaken to evaluate whether such the changes in visceral adipose tissue were detected in patients with DM2. We obtained omental and mesenteric adipose tissue during surgery of lymph node dissection for gastric and colorectal cancers, and investigated these variables in adipose tissue (omental from gastric cancer; 13 non-DM, 12 DM2: mesenteric from colorectal cancer; 12 non-DM, 11 DM2). RESULTS: Acetylation of histone H3K9 at the promoter region of Dbp and DBP mRNA expression in omental, but not in mesenteric adipose tissue were significantly lower in DM2 than in patients without DM. PPAR-γ mRNA expression in omental adipose tissue was also lower in patients with DM2, but not in mesenteric adipose tissue. CONCLUSIONS: The changes in DBP-PPAR-γ axis observed in mice with diabetes were also detected in patients with DM2. Because adiponectin secretion is reported to be enhanced through the PPAR-γ-related mechanism, this study supports the hypothesis that omental adipose tissue is involved in the mechanism of DM2.

[Multimodal therapy improved carcinoid syndrome secondary to liver metastases of an atypical lung carcinoid tumor:a case report].

A 69-year-old male presented for an annual medical examination, and his chest X-ray showed an abnormal shadow. He presented to our hospital, and was diagnosed with typical carcinoid tumor of the lung by bronchoscopy. We recommended surgery, however the patient did not agree to the operation. One year later, two masses were detected in the liver. Ultrasound guided biopsy revealed that they were metastases from the atypical carcinoid tumor of the lung. We recommended chemotherapy, but he refused. Six months later, he was admitted to our hospital for symptoms of flushing, fever, watery diarrhea, and palpitations. We diagnosed this combination of symptoms as carcinoid syndrome, and started the administration of a long acting release (LAR) octreotide. The patient's symptoms improved, but did not resolve completely. We then performed a hepatic artery embolization for the liver metastases, and the symptoms resolved. However, viable lesions of the liver metastases slowly grew and caused a carcinoid crisis. By increasing the dosage of octreotide up to a continuous intravenous infusion of 1500µg/day, as well as LAR 30mg/4weeks, the patient recovered from the crisis. Hepatic artery embolization was performed shortly afterward. Because it was difficult to control the carcinoid syndrome by hepatic artery embolization alone, he underwent a resection of the liver metastases. After the hepatic resection, he has had no recurrence of carcinoid syndrome while still being treated with octreotide LAR.

Single-Drug Approach with Edoxaban is Effective for Resolving Non-Acute Cancer-Associated Venous Thrombosis: A Single-Arm Retrospective Analysis.

Recently, cancer-related venous thromboembolism (VTE) has been termed "cancer-associated thrombosis (CAT)" and is the focus of current research. We retrospectively investigated the efficacy of a single-drug approach with edoxaban for the treatment of non-acute CAT. Thirty-two non-acute CAT patients who received edoxaban were analyzed. The primary endpoint of this analysis was the thrombus disappearance rate at the first evaluation. Secondary endpoints included progression/recurrence of VTE, major bleeding, and D-dimer levels. The thrombus disappearance rate was 62.5%. Therefore, the null hypothesis for the primary endpoint (thrombus disappearance rate of ≤32.0%) was rejected (p = 0.00038) based on the rate of the previous study as the historical control. Recurrent VTE and major bleeding occurred in two patients each. After the start of treatment with edoxaban, a significant difference in D-dimer levels was observed (p = 0.00655). We demonstrated that a single-drug approach with edoxaban is a potential treatment option for non-acute CAT.

Genetic population structure of invasive raccoons (Procyon lotor) in Hokkaido, Japan: Unique phenomenon caused by pet escape or abandonment.

Phylogeographic studies can resolve relationships between genetic population structure of organisms and geographical distributions. Raccoons have become feral in Japan, and in Hokkaido island, they have been rapidly increasing in number and spreading since the 1970s. We analyzed mitochondrial (mtDNA) and microsatellite DNA to understand the current phylogenetic distribution and invasive founder events. Overall, Hokkaido raccoons maintained high genetic diversity (i.e., the level of heterozygosity was comparable to the original habitat, North America). Based on mtDNA distribution and microsatellite diversity, Hokkaido raccoons were divided into six management units. However, mtDNA haplotype distributions and genetic structures based on microsatellites did not always correspond to each other (e.g., two geographically and genetically separated populations showed similar mtDNA distributions). In addition, a high degree of genetic admixture was observed in every unit, and the degree of genetic differentiation was low even between regions separated by long distances. Compared with other countries in Europe where genetic distribution of introduced raccoons is more clearly structured, the current results represent a unique and complex phenomenon of pet escape/abandonment in Hokkaido: i.e., genetically related colonies were introduced into multiple regions as founder events, resulting in the current state in which raccoons are not clearly genetically differentiated even 40 years after introduction.