Prognostic impact of carcinoembryonic antigen in 1822 surgically treated esophageal squamous cell carcinoma: multi-institutional study of the Japan Esophageal Society.

BACKGROUND: Previous studies have evaluated the clinicopathological significance of carcinoembryonic antigen (CEA) of esophageal cancer in relatively small numbers of patients. Therefore, this study aimed to clarify the prognostic significance of CEA in 1822 patients with esophageal squamous cell carcinoma (SCC). METHODS: Based on the Japanese Esophageal Society nationwide multi-institutional retrospective study, a total of 1,748 surgically treated ESCC from 15 hospitals were enrolled to evaluate prognostic impact of preoperative CEA values. Among them, 605 patients were categorized to up-front surgery group, and 1,217 patients were categorized to neoadjuvant therapy group. The CEA threshold for positivity was 3.7 ng/ml. The clinicopathological and prognostic impact of CEA was evaluated by univariate and multivariate analysis in each treatment modality groups. RESULTS: In total, the CEA positive rate was 25.8% (470/1822). CEA-positive status was significantly associated with distant metastasis (P = 0.004) but not associated with other factors. CEA-positive status was associated with poor overall survival (P < 0.001) in univariate analysis as well as multivariate analysis (P = 0.003). CONCLUSIONS: CEA was an independent prognostic determinant of overall survival in esophageal SCC. Based on the subgroup analysis, regardless of the treatment modality, patients with high pretreatment CEA showed poor overall survival.

Different response rates to chemotherapy between Japanese and German esophageal squamous cell carcinoma: patients may be influenced by ERCC1 or ABCB1.

Aim: To find out differences in biomarkers between Japanese and German patients responsible for response after neoadjuvant radio/chemotherapy and survival for esophageal squamous cell carcinoma. Materials & methods: A total of 60 patients from Japan and 127 patients from Germany with esophageal squamous cell carcinoma were analyzed according to three SNPs by real-time PCR. Results: The distribution of the genotypes of ERCC1 rs16115 and ABCB1 C3435T rs1045642 was significantly different between both patients' groups. Japanese patients had significantly less good response to 5-fluorouracil/cisplatin chemotherapy. The influence of the three SNPs on response varied between patients from Japan and Germany. Conclusion: Different expressions of ERCC1 and ABCB1 SNPs of Japanese patients compared with the German patients partially explain the different response.

Columnar metaplasia in the remnant esophagus is a long-term indicator for pneumonia after radical esophagectomy.

BACKGROUND: This study investigated the long-term risk factors for pneumonia after esophageal reconstruction using a gastric tube via the posterior mediastinal route following esophagectomy for esophageal cancer. The influence of columnar metaplasia in the remnant esophagus was specifically assessed. METHODS: Among 225 patients who underwent esophagectomy between January 2004 and December 2010, the subjects were 54 patients who could be followed up for more than 5 years. Routine oncologic follow-up consisted of CT scanning of the abdomen and chest every 4-6 months and annual endoscopy. Data on the occurrence of pneumonia were collected by retrospective review of chest CT scans. Risk factors for pneumonia investigated by univariate and multivariate analyses included the age, gender, diameter of the stapler, length of the intrathoracic remnant esophagus, anastomotic stricture, and presence of columnar metaplasia in the remnant esophagus. RESULTS: The median age was 62.4 years (interquartile range: 55.8-68.0 years). Forty-three patients were men. Pneumonia was detected in 39 patients (72.2%). The incidence of columnar metaplasia in the remnant esophagus increases with time. Anastomotic stricture was significantly related to the absence of columnar metaplasia on endoscopy in the first year after esophagectomy (p = 0.013). Univariate analysis showed that the frequency of pneumonia was significantly related to the intrathoracic remnant esophagus length ≥4.4 cm (p = 0.014), age over 65 years (p = 0.014), and the presence of columnar metaplasia in the remnant esophagus in the fifth year after esophagectomy (p = 0.005). Among them, age over 65 years and the presence of columnar metaplasia in the remnant esophagus in the fifth year after esophagectomy were found to be independent indicators of the postoperative pneumonia by multivariate analysis. CONCLUSION: Pneumonia occurred in 72.2% (39/54) of patients after esophagectomy for esophageal cancer. The presence of columnar metaplasia after esophagectomy is an indicator for pneumonia over the long term.

Improvement in the postoperative course of salvage esophagectomy after definitive chemoradiotherapy.

BACKGROUND/AIMS: The aim of this study was to assess the outcome of salvage esophagectomy with less extensive lymphadenectomy, which we have performed since 2003 to improve high mortality and morbidity of standard salvage esophagectomy. METHODOLOGY: We retrospectively compared the surgical outcome of 15 patients who underwent standard salvage esophagectomy via right thoracotomy for thoracic esophageal cancer between 1993 and 2002 (earlier period) with the results of 11 patients between 2003 and 2011 (later period). RESULTS: There were two mortalities in the earlier period, whereas no patient died in the later period, and there was a lower rate of morbidity. In the later period, there was a significantly shorter SIRS duration, lower CRP on postoperative days 1-5, and higher lymphocyte count on postoperative days 2-4. Long-term survival showed no significant difference between the two periods. CONCLUSIONS: Salvage esophagectomy with less extensive lymphadenectomy might improve the surgical outcome while maintaining long-term survival.

Primary esophageal mucosa-associated lymphoid tissue lymphoma treated by endoscopic submucosal dissection.

Primary esophageal mucosa-associated lymphoid tissue (MALT) lymphoma is rare. There have been few reports about early primary esophageal MALT lymphoma being treated endoscopically. The clinical profile of primary esophageal MALT lymphoma is currently unclear, so it is important to accumulate more information about early esophageal MALT lymphoma. To achieve early detection of esophageal MALT lymphoma, we need more accurate knowledge and information about the macroscopic and morphological features of this tumor. Endoscopic resection is one of the most effective treatments. With respect to the lateral and vertical margins of the resected specimen, endoscopic submucosal dissection (ESD) may be superior to endoscopic mucosal resection for treating early esophageal MALT lymphoma. Here we report the macroscopic appearance of the tumor which is the first successful case of ESD for early esophageal MALT lymphoma.

Prognostic Impact of Serum SCC Antigen in the 566 Upfront Surgery Group of Esophageal Squamous Cell Carcinoma: A Multi-Institutional Study of the Japan Esophageal Society.

PURPOSE: This study aimed to determine the clinicopathologic and prognostic significance of squamous cell carcinoma antigen (SCC-Ag) in patients with esophageal SCC who underwent radical surgery without neoadjuvant therapy. METHODS: This study included 566 patients with primary esophageal SCC who underwent radical resection without neoadjuvant therapy at 15 Japanese hospitals between 2008 and 2016. The cutoff value of SCC-Ag was 1.5 ng/mL based on the receiver operating characteristic curves. Preoperative SCC-Ag and postoperative SCC-Ag were analyzed to evaluate clinicopathological and prognostic significance. Survival curves were compared between the SCC-Ag-positive group and the SCC-Ag-negative group. The prognostic impact of SCC-Ag was evaluated using univariate and multivariate analyses. RESULTS: The preoperative SCC-Ag-positive rate was 23.5% (133/566). SCC-Ag-positive status was significantly associated with old age (p = 0.042), tumor depth (p <0.001), and tumor stages (p <0.001). The preoperative SCC-Ag-positive group had significantly poorer overall survival than the SCC-Ag-negative group (p = 0.030), but it was not an independent predictor of poor prognosis. Postoperative SCC-Ag-positive status was an independent risk factor for poor overall survival (p = 0.034). CONCLUSION: Both pre- and postoperative SCC-Ag-positive statuses were significantly associated with poor prognosis. Postoperative SCC-Ag-positive status was an independent risk factor for predicting overall survival.

Comparative analysis of the outcomes of gastrectomy vs. endoscopic mucosal resection or endoscopic submucosal dissection for the treatment of gastric tube cancer after esophagectomy.

This study investigated the clinical characteristics of patients with gastric tube cancer following esophagectomy at our hospital, and to examine the outcomes of gastrectomy versus endoscopic submucosal dissection. Of 49 patients who underwent treatment for gastric tube cancer that developed 1 year or more after esophagectomy, 30 patients underwent subsequent gastrectomy (Group A), and 19 patients underwent endoscopic mucosal resection (EMR) or endoscopic submucosal dissection (ESD) (Group B). The characteristics and outcomes of these two groups were compared. The interval between esophagectomy and diagnosis of gastric tube cancer ranged from 1 to 30 years. The most common location was the lesser curvature of the lower gastric tube. When the cancer was detected early, EMR or ESD was performed, and the cancer did not recur. In advanced tumors, gastrectomy was performed but the gastric tube was difficult to approach and lymph node dissection was difficult; two patients died as a result of the gastrectomy. In Group A, recurrence occurred most often as axillary lymph node, bone, or liver metastases; in Group B, no recurrence or metastases were observed. In addition to recurrence and metastasis, gastric tube cancer is often observed after esophagectomy. The present findings highlight the importance of early detection of gastric tube cancer after esophagectomy and that the EMR and ESD procedures are safe and have significantly fewer complications compared with gastrectomy. Follow-up examinations should be scheduled with consideration given to the most frequent sites of gastric tube cancer occurrence and the time elapsed since esophagectomy.

[Docetaxel plus S-1 as a second-line chemotherapy for metastasis or recurrence of esophageal cancer].

Although chemotherapy consisting of cisplatin and 5-fluorouracil(CF)has been a standard regimen for esophageal cancer, it might be difficult to use continuously. This study evaluated the response and safety of docetaxel plus S-1 used as a second line therapy. We reviewed 21 patients(postoperatively, 11; after definitive chemoradiotherapy, 8; after chemotherapy, 2) who received chemotherapy between 2006 and 2010. Metastatic or recurrent disease was detected in the organs(n=8), lymph nodes(n=8), main tumors(n=3), mediastinum(n=1), and pleura(n=1). Docetaxel 30mg/m2 was infused every 2 weeks, and S-1 80mg/m2 was taken for 2 weeks, then with 2 weeks rest until progression. Almost all of the patients received docetaxel in the outpatient chemotherapy room. The median number of treatment cycles was 3, ranging from 1-12. Among the 14 patients with a therapeutic response, three(21%)achieved PR, 8 showed SD, and 3 had PD. Toxicity which included grade 3/4 was neutropenia in 6 patients, and anemia in one patient. After a follow-up of over one year, the median overall survival was 10 months, and the one-year survival rate was 38%. Docetaxel plus S-1 might be a feasible regimen as a second-line chemotherapy for metastasis or recurrence of esophageal cancer.

Cardiac metastasis after esophagogastrectomy for esophageal adenocarcinoma with an antemortem diagnosis.

Cardiac metastasis is uncommon and rarely diagnosed antemortem. Here, we describe a case of symptomatic cardiac metastasis from esophageal adenocarcinoma. A 64-year-old man developed chest symptoms 26 months after curative esophagogastrectomy for esophageal adenocarcinoma. Initially, ischemic cardiac disease was suspected based on electrocardiography findings, but an infiltrative tumor was seen morphologically in the wall of the interventricular septum and apex. No other lesions were detected. Histological examination of a transcatheter biopsy specimen indicated that the cardiac tumor was metastasis from esophageal adenocarcinoma. Chemoradiotherapy with cisplatin relieved his symptoms, and he had resumed normal activities. However, he opted not to undergo further aggressive treatment due to severe adverse effects from cisplatin. Seventeen months after completion of chemoradiotherapy, metastases to the right ventricle and the left thighbone were detected and he died 27 and 24 months after the diagnosis of cardiac metastasis and completion of chemoradiotherapy, respectively.

Prognostic Impact of Pretreatment Serum CYFRA Status in 1047 Patients with Esophageal Squamous Cell Carcinoma Who Underwent Radical Resection: A Japan Esophageal Society Promotion Research.

PURPOSE: The prognostic significance of pretreatment serum C-terminus of cytokeratin 19 (CYFRA21-1, CYFRA) status was evaluated in the patients with surgically treated esophageal squamous cell carcinoma. METHODS: A total of 1047 patients with surgically treated esophageal cancer were enrolled in a multi-institutional study promoted by the Japanese Esophageal Society. This study included an up-front surgery group (n = 412), a neoadjuvant chemotherapy (NAC) group (n = 486), and a neoadjuvant chemoradiation/radiation therapy (NACRT/RT) group (n = 149). The pretreatment CYFRA status was analyzed to assess prognostic significance using multivariate analysis according to treatment modalities. RESULTS: The CYFRA-positive group was significantly associated with deep tumor. Univariate analysis showed that the overall survival of the CYFRA-positive group was significantly worse than that of the CYFRA-negative group, but the difference was not significant in the multivariate analysis. CYFRA was an independent risk factor for poor prognosis just in the NACRT/RT group. CONCLUSIONS: The CYFRA-positive group was associated with deep tumor and poor survival. Pretreatment CYFRA was not an independent risk factor for poor prognosis in the up-front surgery group or NAC group. It was an independent risk factor for poor prognosis just in the NACRT/RT group.

Primary lymphoepithelioma-like carcinoma of the esophagus with metastatic lymph node and gastric cancer.

Upper gastrointestinal lymphoepithelioma-like carcinoma (LELC) is a rare disease-especially esophageal LELC (ELELC). Here, we report a surgically treated case of ELELC with gastric carcinoma. The patient was a 68-year-old asymptomatic Japanese man. Endoscopy revealed a submucosal-like protruding tumor located in the anterior wall of the esophagus 31-33 cm from the upper incisors and a slightly ulcerative lesion at the antrum of stomach. Histopathological diagnosis from biopsy of the esophageal lesion revealed a poorly differentiated squamous cell carcinoma; the stomach lesion was found to be well-differentiated tubular adenocarcinoma. CT showed a swollen lymph node along the left recurrent nerve. On the basis of a diagnosis of esophageal and gastric cancer, we performed esophagectomy with three-field lymph node dissection and partial gastrectomy. Histopathology of the resected esophageal tumor revealed solid nests of cancer cells, with substantial infiltration of lymphoid cells into the stroma. There were poorly differentiated cancer cells with large nuclei in the lymph node. In situ hybridization for Epstein-Barr virus showed no nuclear signal in the tumor cells. Immunohistochemistry gave a diagnosis of ELELC.

XRCC1 gene polymorphism for prediction of response and prognosis in the multimodality therapy of patients with locally advanced rectal cancer.

BACKGROUND: Neoadjuvant treatment strategies have been developed to improve survival of patients with locally advanced rectal cancer. Since mainly patients with major histopathologic response benefit from this therapy, predictive markers are needed. The gene polymorphism of the X-ray-repair-cross complementing (XRCC1-) gene (rs25487) was analyzed to predict response to neoadjuvant radiochemotherapy and prognosis in patients with locally advanced rectal cancer. PATIENTS AND METHODS: 81 patients (51 male; 30 female; median age 59 years) with locally advanced rectal cancer were included in this study. All patients received a neoadjuvant radiochemotherapy (50.4 Gy, 5-FU) followed by surgical therapy. Histomorphologic regression was defined as major response when resected specimens contained less than 10% viable tumor cells (n = 28) and minor response when more than 10% viable tumor cells (n = 53) were detected in the surgical specimen. Genomic DNA was extracted from paraffin-embedded tissues of all study patients. Allelic discrimination was performed by real-time polymerase chain reaction. Two allele-specific TaqMan probes in competition were used for amplification of the XRCC1 gene. Allelic genotyping was correlated with therapy response and prognosis. RESULTS: Single-nucleotide polymorphism XRCC1 A399G (rs25487) was predictive for therapy response (P = 0.039). Within the AG genotype group, 17 (53%) patients showed a minor response and 15 (47%) patients a major response. In contrast, 39 (78%) of the patients with homogeneous AA or GG genotype were minor responders and only 11 (22%) major responders. No prognostic value was revealed for the XRCC1 A399G (rs25487) gene polymorphism in the multimodality therapy. CONCLUSION: Our data supports the role of XRCC1 as a predictive marker for therapy response in the multimodality therapy of patients with locally advanced rectal cancer. Single-nucleotide polymorphism XRCC1 A399G (rs25487) could be applied to individualize treatment strategies.

[An appropriate chemotherapy for esophageal cancer from a histological standpoint].

The histology of esophageal cancer represents squamous cell carcinoma mainly in Eastern countries and adenocarcinoma in Western countries. This difference entails differences in treatment strategy. Thus, clinical studies in Japan are necessary, although recent trials showed marvelous progress. By adopting pharmacogenetic approaches for not only biomarkers but also targeting therapies, surgery can be surpassed in the near future.

Multimodal treatment for lymph node recurrence of esophageal carcinoma after curative resection.

BACKGROUND: Although esophagectomy with extended lymph node dissection can improve survival of patients with esophageal carcinoma, lymph node metastasis has remained one of the main recurrence patterns. The aim of this study was to evaluate the outcome of intensive treatment for recurrent lymph node metastasis. METHODS: Recurrent lymph node metastasis was detected in 68 patients with thoracic esophageal carcinoma after curative esophagectomy (R0, International Union Against Cancer criteria). Multimodal treatment was performed in 41 patients: 19 patients underwent lymphadenectomy with adjuvant therapy, and 22 received definitive chemoradiotherapy and repeated chemotherapy. The remaining 27 patients (40%) received chemotherapy or best supportive care. RESULTS: Survival of the lymphadenectomy and the chemoradiotherapy groups was significantly better than that of the patients who received chemotherapy or best supportive care (P < .0001). Fifteen patients (79%) underwent curative lymph node dissection (R0) in the lymphadenectomy group. Complete response, partial response, and stable disease were obtained in 8 (37%), 10 (45%), and 4 (18%) patients who received chemoradiotherapy, respectively. There was no statistically significant difference in survival between the lymphadenectomy and the chemoradiotherapy groups. Although the location of lymph node metastasis did not influence survival significantly, seven patients with nodes around the abdominal aorta did not survive longer than 3 years. The most common repeat recurrence pattern was organ metastasis after the treatment. Multivariate analysis showed that the number of metastatic nodes and tumor marker were independent prognostic factors. CONCLUSION: Multimodal treatment including lymphadenectomy and chemoradiotherapy could improve survival of the patients with lymph node recurrence of esophageal carcinoma after curative resection.

Constant maintenance of an alternative route of coronary flow in radical surgery for gastric cancer following coronary artery bypass grafting involving the right gastroepiploic artery: a case report.

We describe a 64-year-old man diagnosed as having gastric cancer with a patent right gastroepiploic artery (RGEA) used for coronary artery bypass grafting (CABG). Before gastrectomy, the native coronary artery was revascularized to safely dissect the infrapyloric lymphatic tissue along the layer recently identified as an appropriate layer for radical lymphadenectomy, in anticipation of preserving the radically skeletonized RGEA. The perioperative strategy was feasible. Postoperatively, hemorrhage extended the stopping period of antiplatelet therapy. However, since the RGEA was preserved, an alternative route was available for coronary flow. After a 41-month postoperative follow-up, the patient remained in good health, with no recurrence or cardiac ischemia. In this case, the alternative route of coronary flow could be constantly maintained, although radical infrapyloric lymphadenectomy had been performed. Preoperative revascularization and preserving the RGEA with radical skeletonization can be a safe yet permissibly radical strategy for gastric cancer treatment following CABG involving the RGEA.

Incidence of Esophageal Carcinomas After Surgery for Achalasia: Usefulness of Long-Term and Periodic Follow-up.

BACKGROUND Patients with esophageal achalasia are considered to be a high-risk group for esophageal carcinoma, and it has been reported that this cancer often arises at a long interval after surgery for achalasia. However, it is unclear whether esophageal carcinoma is frequent when achalasia has been treated successfully and the patient is without dysphagia. In this study, we reviewed patients with esophageal carcinoma who were detected by regular follow-up after surgical treatment of achalasia.   CASE REPORT Esophageal cancer was detected by periodic upper GI endoscopy in 6 patients. Most of them had early cancers that were treated by endoscopic resection. All 6 patients had undergone surgery for achalasia and the outcome had been rated as excellent or good. Annual follow-up endoscopy was done and the average duration of follow-up until cancer was seen after surgery was 14.3 years (range: 5 to 40 years). Five patients had early cancer. Four cases had multiple lesions.   CONCLUSIONS In conclusion, surgery for achalasia usually improves passage symptoms, but esophageal cancer still arises in some cases and the number of tumors occurring many years later is not negligible. Accordingly, long-term endoscopic follow-up is needed for detection of malignancy at an early stage.

Comparison of extended esophagectomy through mini-thoracotomy/laparotomy with conventional thoracotomy/laparotomy for esophageal cancer.

OBJECTIVE: In order to assess the usefulness of esophagectomy through mini-thoracotomy/laparotomy as a minimally invasive surgical procedure for esophageal cancer, we compared the results to those of conventional right thoracotomy/laparotomy. METHODS: From 1998 to 2002, 40 patients with thoracic esophageal cancer were prospectively assigned to two groups. Twenty patients underwent esophagectomy through mini-thoracotomy/laparotomy (M-group), while the other 20 had conventional thoracotomy/laparotomy (C-group). Surgical complications, the duration of the systemic inflammatory response syndrome (SIRS), postoperative pain, cytokine responses, and respiratory function were compared between the two groups. RESULTS: There was no difference of morbidity between the M- and C-groups after surgery. There were also no differences between the two groups with respect to the operating time, bleeding, and number of dissected lymph nodes. The duration of SIRS was shorter in the M-group than in the C-group (p = 0.055). Use of morphine was lower in the M-group than in the C-group with patient-controlled anesthesia (p = 0.002). The interleukin-6 level of the M-group was lower than that of the C-group at 3, 6 hours, and 3 days after the operation. Recovery of vital capacity by the M-group was better than by the C-group after the operation. Postoperative hospital stay of the M-group was significantly shorter than that of the C-group (p = 0.014). Long-term survival was not different in the two groups. CONCLUSION: Mini-thoracotomy/laparotomy reduces invasiveness and pain compared with conventional thoracotomy/laparotomy for esophagectomy without causing any differences of morbidity or long-term survival.

Esophageal metastasis of renal cancer 10 years after nephrectomy.

The patient was a 65-year-old man, who had undergone right nephrectomy for renal cancer in 2002. At that time, histopathological examination revealed clear cell carcinoma (pT3a, pN0, M0, and pStage III). Postoperatively, he received natural interferon alpha (6 million units 3 times a week) from November 2002 to February 2005, and showed no evidence of recurrence. However, he noticed dysphagia in March 2012. Endoscopy revealed a pedunculated polypoid tumor in the mid-esophagus and biopsies were taken showing a clear cell carcinoma. Contrast-enhanced thoracoabdominal CT scanning identified a pedunculated polypoid tumor in the mid-thoracic esophagus and enlargement of a lymph node adjacent to the right main bronchus. With a diagnosis of esophageal and lymph node metastases of renal cancer, the patient underwent esophagectomy with right thoracotomy with reconstruction by a posterior mediastinal stomach tube. Postoperative histopathological examination revealed clear cell carcinoma. Because esophageal metastasis of renal cancer is extremely rare, this case is reported here together with discussions of the relevant literature.

[Nedaplatin and 5-fluorouracil combined with radiotherapy for advanced esophageal cancer].

We conducted a pilot study of nedaplatin + 5-fluorouracil (5-FU) combined with radiotherapy for 29 patients with primary advanced (stage IV) esophageal cancer. A complete remission (CR) was obtained in 4 (14%) and a partial response in 13 patients (response rate: 59%). The median survival time and one-year survival rate were 238 days and 34.5%, respectively. Of the 29 patients, 24 (83%) completed the treatment schedule and toxicity of stomatitis and the like was infrequent. In conclusion, these results suggest that the efficacy of nedaplatin + 5-FU combined with radiotherapy might not differ from that of cisplatin + 5-FU combined with radiotherapy. Clearly, the usefulness of this combined therapy needs to be assessed in multicenter phase III trials.

HER2-positive gastric cancer with paraaortic nodal metastasis successfully resected after chemotherapy with trastuzumab: a case report.

We report on a case of human epidermal growth factor receptor-2 (HER2)-positive gastric cancer with paraaortic lymph node metastasis. The patient (a 49-year-old female) received chemotherapy (capecitabine and cisplatin) plus molecular-targeted therapy (trastuzumab), followed by curative resection. Interestingly, the resected residual cancer was HER2-negative. Intra-tumor heterogeneity hinders molecular-targeted therapy for gastric cancer. In our case, continued trastuzumab administration presented few benefits since the residual cancer cells were HER2-negative. No consensus exists regarding the appropriate therapy for unresectable gastric cancers whose non-curative factors disappear following trastuzumab chemotherapy. The principal options are treatment with surgery or continued chemotherapy with trastuzumab. In our case, resection treated the HER2-negative residual cancer effectively, resulting in curative therapy. This is the first case of positive-to-negative change in the HER2 expression of residual tumor cells following trastuzumab therapy. It suggests that, due to intra-tumor heterogeneity, the risks presented by remnant HER2-negative cancer cells persist despite trastuzumab therapy.