Safety of immune checkpoint inhibitors after proton beam therapy in head and neck mucosal melanoma: a case series.

Proton beam therapy (PBT) has shown promising efficacy in treating locally advanced head and neck mucosal melanoma despite its poor prognosis. Although PBT may improve the efficacy of subsequent immune checkpoint inhibitors (ICIs), the safety of ICIs in patients who have previously received PBT has not been established. Hence, this study evaluated the safety of ICIs in patients who had recurrent mucosal melanoma after PBT. Between April 2013 and June 2022, we retrospectively reviewed the medical records of patients diagnosed with cutaneous or mucosal melanoma at the National Cancer Center Hospital East. Seven patients were treated with ICIs after their head and neck mucosal melanoma (HNMM) recurred after PBT. Four of the seven patients experienced grade immune-related adverse events (irAEs). Due to irAE in the irradiation field, two patients had grade 3 hypopituitarism. Other grade 3 or higher irAEs included an increase in serum alanine aminotransferase in two patients and gastritis in one, and two patients discontinued ICI due to the irAEs. All irAEs were resolved with appropriate management. Although administering ICIs after PBT may increase the risk of irAEs, especially in the irradiation field, they appear manageable. These findings could help in the development of a treatment strategy for locally advanced HNMM that includes PBT and subsequent ICIs.

Mitigation of paclitaxel-induced peripheral neuropathy in breast cancer patients using limb-cooling apparatus: a study protocol for a randomized controlled trial.

Background: Chemotherapy-induced peripheral neuropathy (CIPN) is one of the most common adverse events that can significantly impair the quality of life of patients. Although limb cooling may be beneficial for preventing CIPN, logistical challenges exist in ensuring consistent efficacy and safety. The purpose of this randomized controlled trial is to validate whether limb cooling with strict temperature control can reduce CIPN in patients with breast cancer receiving weekly paclitaxel as a perioperative treatment. Methods: This study is a multicenter, double-blinded, randomized controlled trial. We plan to enroll patients with breast cancer who are scheduled to receive 12 weekly doses of paclitaxel (60 min 80 mg/m2 intravenous infusion) as perioperative chemotherapy. Patients will be randomly divided into the intervention or control groups and undergo limb cooling therapy maintained at a constant temperature of 13°C and 25°C, respectively. The primary endpoint is the proportion of patients who report Patient Neurotoxicity Questionnaire (PNQ) ≥ D in their limbs by the end of the study treatment or at the time of discontinuation. Discussion: The results of this trial will contribute to the establishment of new evidence for limb cooling therapy in the mitigation of CIPN and present a safe and stable cooling device that may be suitable for use in the clinic. Clinical trial registration: https://jrct.niph.go.jp/en-latest-detail/jRCT2032210115, identifier jRCT2032210115.

The impact of the COVID-19 pandemic on perioperative chemotherapy for breast cancer.

BACKGROUND: Since it was first reported in December 2019, coronavirus disease 2019 (COVID-19) spread rapidly across the globe resulting in a pandemic. As of August 2022, seven outbreak peaks have been confirmed in Tokyo, and the numbers of new cases in the fifth and later outbreak periods have been far greater than in the preceding periods. This retrospective study examined the impact of the COVID-19 pandemic on perioperative chemotherapy for breast cancer. METHODS: Patients with breast cancer who received perioperative chemotherapy at the National Cancer Center Hospital East were divided into 2 groups: 120 and 384 patients who started chemotherapy before and during the pandemic, respectively. The incidence of critical events that had potential detrimental effects on the prognosis, such as start of adjuvant chemotherapy ≥91 days after surgery and relative dose intensity of chemotherapy <85% were compared between groups. RESULTS: No significant difference in the incidence of critical events was found. When stratified by outbreak period, the incidence of critical events was positively correlated with the increasing number of new cases of COVID-19 (r = 0.83, p = 0.04). Moreover, 25/173 patients (14%) who started perioperative chemotherapy during the fifth and sixth outbreak periods developed COVID-19 infection, 80% of whom (20/25) had a delay or interruption to their surgery or other perioperative treatments. CONCLUSIONS: Although the impact of the COVID-19 pandemic on perioperative chemotherapy on whole groups of patients was not evident when comparing periods before and after the pandemic, the impact is becoming prominent in parallel with increasing numbers of new COVID-19 cases.

Clinical features of CDK4/6 inhibitor-related interstitial lung disease in patients with breast cancer: a case series study.

BACKGROUND: Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors are the standard treatment for advanced hormone receptor-positive breast cancer. Although interstitial lung disease is a rare (1-3.3%) but serious adverse event associated with CDK4/6 inhibitors, the incidence of interstitial lung disease in Japanese patients in the real world and the risk factors of interstitial lung disease are not clear. METHODS: We retrospectively investigated the incidence of interstitial lung disease in 224 patients with advanced breast cancer who received CDK4/6 inhibitors at our hospital between 31 January 2017 and 31 January 2021. The correlation of age (>50 vs ≤50 years), presence or absence of previous history of interstitial lung disease, lung metastasis, smoking history and chest radiation with the development of interstitial lung disease was evaluated. RESULTS: In total, 177 cases received palbociclib, 39 cases received abemaciclib and 8 cases received both palbociclib and abemaciclib, constituting a palbociclib group (n = 185) and an abemaciclib group (n = 47). At a median observation period of 607 days, 8.0% (18/224) cases (13 definite and 5 probable cases) had interstitial lung disease; 6.5% (12/185) of palbociclib-treated and 13% (6/47) of abemaciclib-treated cases. The median time to interstitial lung disease onset was 178 (range, 14-750) days. There was no significant correlation between the background factors studied and the development of interstitial lung disease. CONCLUSION: The frequency of CDK4/6 inhibitor-induced interstitial lung disease was higher than that reported in clinical trials. We did not identify any risk factors for the development of interstitial lung disease in this study, and thus, larger studies that include patient predisposition are required.

Impact of Older Age and Medico-social Factors on the Decision to Offer Adjuvant Chemotherapy to Patients With Breast Cancer.

BACKGROUND/AIM: Although clinicians are expected to set a higher threshold for administering adjuvant chemotherapy to older than younger patients with breast cancer, the extent to which older patients are less likely to be offered adjuvant chemotherapy and the medico-social factors that influence decision-making are unclear. PATIENTS AND METHODS: We retrospectively evaluated the correlations of clinicopathological factors, including age (≥75 years vs. <75 years), for all candidates for adjuvant chemotherapy, and of additional medico-social factors, including the number of family members living together, for older patients, with the rate of referral from breast surgeons to medical oncologists. RESULTS: Among 872 candidates for adjuvant chemotherapy, age ≥75 years was significantly correlated with a lower referral rate (24 % vs. 44%, p<0.001). In the analysis by age group, we did not identify specific medicosocial factors that were differentially emphasized, but older patients who lived with ≥2 other family members tended not to be referred to a medical oncologist compared to those who lived alone or with one family member (1/23 vs. 15/47). Although 5 of 22 older patients (23%) who were referred to a medical oncologist actually received adjuvant chemotherapy (vs. 60% of younger patients), all needed treatment modifications. CONCLUSION: Breast surgeons regard age ≥75 years as a key factor for avoiding adjuvant chemotherapy but they also consider similar medico-social factors irrespective of the patient's age regarding the decision to refer patients to medical oncologists.

Transcriptomic profiling of single circulating tumor cells provides insight into human metastatic gastric cancer.

Transcriptome analysis of circulating tumor cells (CTCs), which migrate into blood vessels from primary tumor tissues, at the single-cell level offers critical insights into the biology of metastasis and contributes to drug discovery. However, transcriptome analysis of single CTCs has only been reported for a limited number of cancer types, such as multiple myeloma, breast, hepatocellular, and prostate cancer. Herein, we report the transcriptome analysis of gastric cancer single-CTCs. We utilized an antigen-independent strategy for CTC isolation from metastatic gastric cancer patients involving a size-dependent recovery of CTCs and a single cell isolation technique. The transcriptomic profile of single-CTCs revealed that a majority of gastric CTCs had undergone epithelial-mesenchymal transition (EMT), and indicated the contribution of platelet adhesion toward EMT progression and acquisition of chemoresistance. Taken together, this study serves to employ CTC characterization to elucidate the mechanisms of chemoresistance and metastasis in gastric cancer.

Impacts of clinicopathological factors on efficacy of trastuzumab deruxtecan in patients with HER2-positive metastatic breast cancer.

BACKGROUND: The previous second-line treatment for HER2-positive metastatic breast cancer were ado-trastuzumab emtansine (T-DM1); however, its activity is decreased in tumors with heterogenous, reduced, or loss of HER2 expression. Trastuzumab deruxtecan (T-DXd) has recently been developed as a novel antibody-drug conjugate to overcome resistance to T-DM1. However, clinical evidence on its ability to overcome this resistance is limited. MATERIALS AND METHODS: We retrospectively analyzed data for patients with HER2-positive metastatic breast cancer who received T-DXd at our institution from April 2020 to March 2021. We evaluated the associations between clinicopathological and molecular biomarkers and the efficacy of T-DXd. RESULTS: Twenty-two patients were enrolled in this study. The median progression-free survival (PFS) was 9.7 months (95% confidence interval [CI], 7.0-not reached [NR]), and the objective response rate (ORR) was 61.9%. The ORR and PFS were comparable between patients with HER2 immunohistochemistry scores of 3+ and 2+/1+ at initial diagnosis (ORR: 50.0% vs. 72.7%, p = 0.39; median PFS, 9.7 months [95%CI, 2.6-NR] vs. 8.3 months [95%CI, 7.1-NR]; hazard ratio, 1.86 [95%CI, 0.53-6.57], p = 0.34). Two patients with heterogenous HER2 expression had a partial response or long stable disease (≥6 months). Three of four patients with re-biopsy samples after anti-HER2 targeted therapy and with latest HER2 immunohistochemistry scores of 1+ experienced partial responses (75.0%) to T-DXd, but none had responded to prior T-DM1. CONCLUSIONS: T-DXd demonstrated favorable activity in clinical practice. Moreover, T-DXd showed meaningful benefit in patients with heterogeneity, reduction, or loss of HER2 expression.

Comparison of Treatment Completion Rate Between Conventional and Dose-dense Doxorubicin and Cyclophosphamide (AC) Followed by a Taxane in Patients With Breast Cancer: A Propensity Score-matched Analysis.

BACKGROUND/AIM: To maximize the effect of perioperative chemotherapy in breast cancer, it is critical to keep the relative dose intensity (RDI) high. While bi-weekly doxorubicin and cyclophosphamide, dose-dense AC (ddAC), instead of tri-weekly conventional AC (cAC) followed by a taxane has been adopted as standard perioperative chemotherapy, postponement or discontinuation are sometimes experienced during ddAC or subsequent taxane phase. This study aimed at evaluating whether ddAC, compared to cAC, was associated with reduced RDI. PATIENTS AND METHODS: We compared ddAC and cAC, both followed by a taxane, for perioperative breast cancer regarding the proportion of completion of planned treatment (%completion), defined as an RDI ≥85% for both AC and taxane phases. RESULTS: There was no remarkable difference between the groups in patient characteristics after propensity score matching (n=46 in ddAC, and n=86 in cAC). The %completion was similar between the groups (67.4% vs. 65.1%). Most other endpoints related to RDI were similar between groups. The incidence of pneumonia was higher in the ddAC group (13% vs. 3%) including one Pneumocystis jiroveci pneumonia. CONCLUSION: ddAC followed by a taxane can be considered with sufficient supportive measures and precautions for pneumonia.

The efficacy and safety of paclitaxel plus bevacizumab therapy in breast cancer patients with visceral crisis.

BACKGROUND: Visceral crisis in metastatic breast cancer (MBC) is defined as severe organ dysfunction requiring rapidly efficacious therapy. Although weekly paclitaxel plus bevacizumab (wPTX + BV) achieves a high response rate in human epidermal growth factor receptor 2 (HER2)-negative MBC, the efficacy and safety of wPTX + BV for visceral crisis is unclear. METHODS: We retrospectively investigated patients with MBC with visceral crisis who received wPTX + BV. Visceral crisis was defined as follows: liver dysfunction (aspartate or alanine aminotransferase >200 U/L or total bilirubin >1.5 mg/dl), respiratory dysfunction (carcinomatous lymphangiomatosis, SpO2 <93% in ambient air or required thoracentesis), superior vena cava (SVC) syndrome, or bone marrow carcinomatosis. The primary outcome was the proportion of patients on-treatment with wPTX + BV after 12 weeks. We also investigated time to treatment failure (TTF), overall survival (OS), objective response rate (ORR), and adverse events. RESULTS: A total of 44 patients with respiratory dysfunction (n = 29), liver dysfunction (n = 10), bone marrow carcinomatosis (n = 7), and SVC syndrome (n = 2) were eligible for this investigation. The proportion of patients on-treatment with wPTX + BV after 12 weeks was 63% (30/44), and the other patients discontinued wPTX + BV because of adverse events (n = 5) and disease progression (n = 9). Median TTF and OS, and the ORR were 131 days and 323 days, and 41%, respectively. No treatment-related death occurred. CONCLUSION: wPTX + BV achieved favorable efficacy and safety for treating patients with visceral crisis and may therefore be considered an option for the treatment of this acutely severe clinical condition.

Effects of Ado-Trastuzumab Emtansine and Fam-Trastuzumab Deruxtecan on Metastatic Breast Cancer Harboring HER2 Amplification and the L755S Mutation.

Somatic mutations in human epidermal growth factor receptor 2 (HER2) are present in approximately 3% of breast cancers. Some HER2 mutations are activating, and they represent a mechanism of resistance to conventional anti-HER2 therapies such as trastuzumab and lapatinib. Consistently, in patients with HER2-amplified breast cancer, these mutations are predominantly observed in metastatic tumors obtained after exposure to anti-HER2 systemic therapies, possibly after clonal selection. Therefore, it is rare to find coexistent HER2 mutation and amplification in the early clinical course, and thus, the clinical relevance of HER2 mutation to the sensitivity to HER2-targeted drugs, particularly antibody-drug conjugates (ADCs) such as ado-trastuzumab emtansine (T-DM1) and the recently approved fam-trastuzumab deruxtecan (T-DXd), remains unclear. In this article, we describe a patient with de novo metastatic breast cancer who exhibited both HER2 amplification and the L755S mutation in the untreated primary breast tumor obtained at the initial diagnosis, and the lesion responded to T-DM1 and T-DXd after exhibiting clinical resistance to other HER2-targeted drugs. Our current case findings suggested that anti-HER2 ADCs should be prioritized over conventional trastuzumab- or lapatinib-based therapies for patients with HER2-amplified and comutated tumors. KEY POINTS: Although HER2 mutations were implicated in resistance to anti-HER2 monoclonal antibodies or HER2 tyrosine kinase inhibitors in preclinical studies, their clinical impact on sensitivity to anti-HER2 drugs is unclear owing to the rarity of concomitant HER2 mutation and HER2 amplification. A case of de novo metastatic breast cancer harboring both HER2 amplification and the L755S mutation in an untreated breast primary tumor displayed clinical resistance to standard trastuzumab- or lapatinib-based therapies but good responses to ado-trastuzumab emtansine (T-DM1) and fam-trastuzumab deruxtecan (T-DXd). Anti-HER2 antibody-drug conjugates such as T-DM1 and T-DXd may be prioritized over conventional trastuzumab- or lapatinib-containing therapies for patients with HER2-amplified and comutated tumors.

[Efficacy of Amrubicin Monotherapy for Patients with Extrapulmonary Neuroendocrine Carcinomas Refractory to Platinum-Based Chemotherapy].

Standard regimens for extrapulmonary neuroendocrine carcinomas(EPNEC)are not established. Treatment used for small cell lung cancer is also used for EPNECs. Amrubicin(AMR) monotherapy is used as salvage therapy for small cell lung cancer, but its efficacy in EPNEC is not clear. The aim of this study was to estimate the efficacy of AMR monotherapy in EPNEC. We retrospectively investigated patients with EPNEC who received first-line platinum-based chemotherapy between April 2007 and March 2019. The time to treatment failure(TTF)and the efficacy and toxicity was analyzed in the patients who received AMR monotherapy. Among 43 patients with EPNEC, 14(13 males, one female; median age, 58 years)received AMR monotherapy. Primary site included the pancreas(n=3), stomach(n=3), rectum(n=1), anal canal(n=1), salivary glands(n= 1), urothelial(n=1), bladder(n=1), prostate(n=1), and 2 patients had primary unknown cancer. Pathological type included small cell(n=4), large cell(n=2), and other types(n=8). Prior chemotherapy comprised CDDP plus CPT-11(n =5), CDDP plus ETP(n=2), and CBDCA plus ETP(n=6). The median TTF was 49(20-61)days. One patient had a partial response and the disease control rate was 33%. The common adverse events of >Grade 3 were leukopenia(69%), neutropenia(62%), and febrile neutropenia(23%). AMR monotherapy was clinically effective and safe for EPNEC.

Bone marrow metastasis of glioblastoma multiforme mimicking acute myeloid leukemia.

A 46-year-old female patient with glioblastoma multiforme (GBM), IDH wild type developed severe pancytopenia 5 months after postoperative chemoradiotherapy. Bone marrow aspirate showed normocellular marrow with 70.0% abnormal cells, which suggested the possibility of acute myeloid leukemia. Immunophenotypic analysis did not show any hematological lineage markers, except for cluster of differentiation 56. The results of immunohistochemical staining of glial fibrillary acidic protein and oligodendrocyte transcription Factor 2 were positive. Based on these findings, the patient was diagnosed with bone marrow metastasis from GBM. Bone marrow metastasis from GBM is rare and little is known about the morphological characteristics of bone marrow aspiration smear findings. We experienced a rare case with marrow metastasis from GBM mimicking acute myeloid leukemia.

[Clinical Efficacy of mFOLFOX6 for Advanced Gastric Cancer].

FOLFOX therapy has been used for gastric cancer in Japan since 2017. We retrospectively analyzed the efficacy of FOLFOX therapy compared to that of FP. Forty-seven cases were evaluated between January 2010 and December 2018. Eighteen patients received mFOLFOX6 therapy, and 29 patients received FP therapy. The median time to treatment failure was 206 days in the mFOLFOX6 group and 58 days in the FP group. The response rate was 50% in the mFOLFOX6 group and 17% in the FP group. Neutropenia(56%), thrombocytopenia(50%), and peripheral neuropathy(56%)were the common adverse events in the mFOLFOX6 group, and leukopenia(69%)and neutropenia(69%)were the common adverse effects in the FP group. Based on our results, we conclude that, unlike FP, FOLFOX is an effective therapy for of gastric cancer.

Clinical impact of controlling nutritional status score on the prognosis of patients with diffuse large B-cell lymphoma.

The controlling nutritional status (CONUT) score is a nutritional index calculated from serum albumin and total cholesterol levels and lymphocyte counts. Its role in predicting clinical outcomes of diffuse large B-cell lymphoma (DLBCL) has not been evaluated. In this retrospective study, data from 476 patients with DLBCL were analyzed. The cutoff value of the CONUT score was set as 4. CONUT score significantly stratified the overall survival (OS) and the progression-free-survival (PFS) (5-year OS, 49.0% vs 83.2%, P < .001; 5-year PFS, 46.1% vs 73.1%, P < .001) of the patients. Among patients at high-intermediate or high risk, as per the National Comprehensive Cancer Network International Prognostic Index (NCCN-IPI), 5-year OS was lower in patients with high CONUT scores than in those with low CONUT scores (high-intermediate risk, 51.2% vs 75.5%, P < .001; high risk, 29.9% vs 63.3%, P = .007). Additionally, in patients with high CONUT scores, maintenance of relative dose intensity (RDI) of chemotherapy did not affect the 5-year OS (RDI > 80% vs RDI ≤ 80%: 59.8% vs 50.9%, P = .73). In the present study, we have demonstrated that the CONUT score is an independent prognostic factor in patients with DLBCL.

Modified FOLFOX-6 Plus Bevacizumab Chemotherapy for Metastatic Colorectal Cancer in Patients Receiving Hemodialysis: A Report of Three Cases and Review of the Literature.

Fluorouracil plus oxaliplatin (L-OHP) (FOLFOX) plus bevacizumab (BV) therapy is commonly administered to patients with metastatic colorectal cancer. However, few reports have described L-OHP therapy in hemodialysis patients, and the efficacy and safety remain uncertain in this population. Here, we report three cases of hemodialysis patients with colorectal cancer who received a modified FOLFOX-6 (mFOLFOX-6, or FOLFOX plus folinic acid) plus BV regimen every 3 weeks. One patient, a 65-year-old man with chronic renal failure consequent to diabetic nephropathy, underwent hemodialysis 3 times/week. He exhibited a partial response after 7 cycles of mFOLFOX-6 plus BV, with the major adverse events of Grade 1 peripheral neuropathy and Grade 2 thrombocytopenia. He died of perforation-related septic shock. A 71-year-old man previously treated with bosutinib for chronic myelocytic leukemia received 9 cycles of mFOLFOX-6 plus BV and achieved stable disease. Chemotherapy was administered every 4 weeks, and the 5-fluorouracil dose was reduced after he developed Grade 4 neutropenia. A 71-year-old woman with chronic renal failure consequent to diabetic nephropathy underwent hemodialysis 3 times a week. She received 3 cycles of mFOLFOX-6 plus BV, but exhibited disease progression and developed Grade 4 neutropenia, which necessitated a reduced 5-fluorouracil dose. After completing FOLFOX therapy, she began second-line irinotecan/5-fluorouracil/leucovorin (FOLFIRI) plus BV therapy. In two cases, bone marrow suppression increased the difficulty of L-OHP dose escalation. We conclude that mFOLFOX-6 plus BV, with appropriate dose reduction, is acceptable for patients with chronic renal failure. Further data are needed to determine the adequate chemotherapy dose.

Multimodal Treatment of Extragonadal Choriocarcinoma with Multiple Brain and Lung Metastases: A Case Report.

Choriocarcinoma is a highly aggressive germ cell tumor and can metastasize to the brain. Although brain metastasis has a poor prognosis, the optimal treatment strategy remains unclear due to its low incidence. A 33-year-old man presenting with multiple lung nodules on chest radiography was referred to our hospital. Computed tomography revealed bilateral lung nodules and a large pelvic mass, and brain magnetic resonance imaging (MRI) demonstrated multiple brain lesions. He developed progressive headache and nausea and underwent two craniotomies because of rapid tumor growth and intratumoral hemorrhage. Metastasis of choriocarcinoma was strongly suspected because of histological findings and detection of urine human chorionic gonadotropin (hCG). He immediately received chemotherapy with bleomycin, etoposide, and cisplatin (BEP). Although the pelvic mass and pulmonary lesions reduced in size and the ß-hCG level decreased after one cycle of BEP, brain MRI displayed an increase in the size and number of brain metastases. He underwent whole-brain radiotherapy (WBRT) concurrently with 2 cycles of BEP, leading to successful reduction of brain metastases. After 4 cycles of BEP, the ß-hCG level was still higher than the normal range, and the pelvic and pulmonary lesions remained. He continued chemotherapy with paclitaxel, ifosfamide, and cisplatin (TIP) and etoposide, ifosfamide, and cisplatin (VIP). The ß-hCG level normalized, and the residual pelvic mass was resected, revealing no viable cancer cells. Multimodal treatment, including two craniotomies and chemotherapy concurrent with WBRT, can achieve good control of lesions of the brain and other sites.

A new prognostic score comprising lactate dehydrogenase, albumin and neutrophil to lymphocyte ratio to predict sensitivity to first-line chemotherapy in patients with peripheral T-cell lymphomas.

No standard therapy for peripheral T-cell lymphomas (PTCLs) has been established, and treatment outcomes are poor. Upfront stem cell transplantation has been investigated in several studies, some of which have reported promising outcomes. However, some patients maintain long-term remission after chemotherapy alone. It is thus important to predict sensitivity to first-line chemotherapy to optimize treatment strategies. In the present study, we retrospectively analyzed time to treatment failure (TTF) of first-line chemotherapy in 59 patients with PTCLs. On multivariate analysis for TTF, elevated lactate dehydrogenase level, hypoalbuminemia, and high neutrophil-to-lymphocyte ratio were significant prognostic factors. Using these three factors, we also developed a new model that effectively distinguished patient outcomes. The TTF rate at 1 year from diagnosis was 71.4% in patients with score 0 (0 factor), 31.8% with score 1 (1 factor) and 4.5% with score 2 (2-3 factors) (P < 0.001). The prognostic power was superior to that of the Prognostic Index for PTCL-unspecified score. Patients with scores of 1 and 2 had poor TTF, and may be candidates for upfront stem cell transplantation if they respond to first-line chemotherapy. Further investigation in a larger cohort is warranted to determine the general applicability of this score.

CD49f(high) cells retain sphere-forming and tumor-initiating activities in human gastric tumors.

Identification of gastric tumor-initiating cells (TICs) is essential to explore new therapies for gastric cancer patients. There are reports that gastric TICs can be identified using the cell surface marker CD44 and that they form floating spheres in culture, but we could not obtain consistent results with our patient-derived tumor xenograft (PDTX) cells. We thus searched for another marker for gastric TICs, and found that CD49f(high) cells from newly-dissected gastric cancers formed tumors with histological features of parental ones while CD49f(low) cells did not when subcutaneously injected into immunodeficient mice. These results indicate that CD49f, a subunit of laminin receptors, is a promising marker for human gastric TICs. We established a primary culture system for PDTX cells where only CD49f(high) cells could grow on extracellular matrix (ECM) to form ECM-attaching spheres. When injected into immunodeficient mice, these CD49f(high) sphere cells formed tumors with histological features of parental ones, indicating that only TICs could grow in the culture system. Using this system, we found that some sphere-forming TICs were more resistant than gastric tumor cell lines to chemotherapeutic agents, including doxorubicin, 5-fluorouracil and doxifluridine. There was a patient-dependent difference in the tumorigenicity of sphere-forming TICs and their response to anti-tumor drugs. These results suggest that ECM plays an essential role for the growth of TICs, and that this culture system will be useful to find new drugs targeting gastric TICs.