Placebo-controlled trial of safety and efficacy of intraoperative controlled delivery by biodegradable polymers of chemotherapy for recurrent gliomas. The Polymer-brain Tumor Treatment Group

Antitumor effect of fibrin glue containing temozolomide against malignant glioma

Temozolomide (TMZ), used to treat glioblastoma and malignant glioma, induces autophagy, apoptosis and senescence in cancer cells. We investigated fibrin glue (FG) as a drug delivery system for the local administration of high-concentration TMZ aimed at preventing glioma recurrence. Our high-power liquid chromatography studies indicated that FG containing TMZ (TMZ-FG) manifested a sustained drug release potential. We prepared a subcutaneous tumor model by injecting groups of mice with three malignant glioma cell lines and examined the antitumor effect of TMZ-FG. We estimated the tumor volume and performed immunostaining and immunoblotting using antibodies to Ki-67, cleaved caspase 3, LC3 and p16. When FG sheets containing TMZ (TMZ-FGS) were inserted beneath the tumors, their growth was significantly suppressed. In mice treated with peroral TMZ plus TMZ-FGS the tumors tended to be smaller than in mice whose tumors were treated with TMZ-FGS or peroral TMZ alone. The TMZ-FGS induced autophagy, apoptosis and senescence in subcutaneous glioma tumor cells. To assess the safety of TMZ-FG for normal brain, we placed it directly on the brain of living mice and stained tissue sections obtained in the acute and chronic phase immunohistochemically. In both phases, TMZ-FG failed to severely damage normal brain tissue. TMZ-FG may represent a safe new drug delivery system with sustained drug release potential to treat malignant glioma.

The combination of carmustine wafers and fotemustine in recurrent glioblastoma patients: a monoinstitutional experience

Background. To date, there is no standard treatment for recurrent glioblastoma. We analyzed the feasibility of second surgery plus carmustine wafers followed by intravenous fotemustine. Methods. Retrospectively, we analyzed patients with recurrent glioblastoma treated with this multimodal strategy. Results. Twenty-four patients were analyzed. The median age was 53.6; all patients had KPS between 90 and 100; 19 patients (79%) performed a gross total resection > 98% and 5 (21%) a gross total resection > 90%. The median progression-free survival from second surgery was 6 months (95% CI 3.9–8.05) and the median OS was 14 months (95% CI 11.1–16.8 months). Toxicity was predominantly haematological: 5 patients (21%) experienced grade 3-4 thrombocytopenia and 3 patients (12%) grade 3-4 leukopenia. Conclusion. This multimodal strategy may be feasible in patients with recurrent glioblastoma, in particular, for patients in good clinical conditions.

Assessing response using 99mTc-MIBI early after interstitial chemotherapy with carmustine-loaded polymers in glioblastoma multiforme: preliminary results

Introduction. Early signs of response after applying wafers of carmustine-loaded polymers (gliadel) are difficult to assess with imaging because of time-related imaging changes. (99m)Tc-sestamibi (MIBI) brain single-photon emission tomography (SPET) has reportedly been used to reveal areas of cellularity distinguishing recurrent neoplasm from radionecrosis. Our aim was to explore the role of MIBI SPET in assessing response soon after gliadel application in glioblastoma multiforme (GBM). Methods. We retrospectively reviewed the charts on 28 consecutive patients with a radiological diagnosis of GBM who underwent MIBI SPET/CT before surgery (with intracavitary gliadel placement in 17 patients), soon after surgery, and at 4 months. The area of uptake was selected using a volume of interest that was then mirrored contralaterally to obtain a semiquantitative ratio. Results. After adjusting for ratio at the baseline, the effect of treatment (gliadel versus non-gliadel) was not statistically significant. Soon after surgery, however, 100% of patients treated with gliadel had a decreased ratio, as opposed to 62.5% of patients in the non-gliadel group (P = 0.0316). The difference between ratios of patients with radical versus partial resection reached statistical significance by a small margin (P = 0.0528). Conclusions. These data seem to suggest that the MIBI ratio could be a valuable tool for monitoring the effect of gliadel early after surgery.

Central nervous system cancers

Primary and metastatic tumors of the central nervous system are a heterogeneous group of neoplasms with varied outcomes and management strategies. Recently, improved survival observed in 2 randomized clinical trials established combined chemotherapy and radiation as the new standard for treating patients with pure or mixed anaplastic oligodendroglioma harboring the 1p/19q codeletion. For metastatic disease, increasing evidence supports the efficacy of stereotactic radiosurgery in treating patients with multiple metastatic lesions but low overall tumor volume. These guidelines provide recommendations on the diagnosis and management of this group of diseases based on clinical evidence and panel consensus. This version includes expert advice on the management of low-grade infiltrative astrocytomas, oligodendrogliomas, anaplastic gliomas, glioblastomas, medulloblastomas, supratentorial primitive neuroectodermal tumors, and brain metastases. The full online version, available at NCCN. org, contains recommendations on additional subtypes.

Key determinants of short-term and long-term glioblastoma survival: a 14-year retrospective study of patients from the Hermelin Brain Tumor Center at Henry Ford Hospital

OBJECTIVE

Glioblastoma (GBM) is a heterogeneous neoplasm with a small percentage of long-term survivors. Despite aggressive surgical resection and advances in radiotherapy and chemotherapy, the median survival for patients with GBM is 12-14 months. Factors associated with a favorable prognosis include young age, high performance status, gross resection >98%, non-eloquent tumor location and O6-methylguanine methyltransferase (MGMT) promoter methylation. We retrospectively analyzed the relationship of clinical, epidemiologic, genetic and molecular characteristics with survival in patients with GBM.

METHODS

This retrospective analysis of overall survival looked at the outcomes of 480 patients diagnosed with GBM over 14 years at a single institution. Multivariate analysis was performed examining multiple patient characteristics.

RESULTS

Median survival time improved from 11.8 months in patients diagnosed from 1995 to 1999 to 15.9 months in those diagnosed from 2005 to 2008. Factors associated with survivor groups were age, KPS, tumor resection, treatment received and early progression. 18 cancer-related genes were upregulated in short-term survivors and five genes were downregulated in short-term survivors.

CONCLUSIONS

Epidemiologic, clinical, and molecular characteristics all contribute to GBM prognosis. Identifying factors associated with survival is important for treatment strategies as well as research for novel therapeutics and technologies. This study demonstrated improved survival for patients over time as well as significant differences among survivor groups.

Radiosensitization of malignant gliomas following intracranial delivery of paclitaxel biodegradable polymer microspheres

OBJECT

The aim of this study was to demonstrate that paclitaxel could function as a radiosensitizer for malignant glioma in vitro and in vivo.

METHODS

The radiosensitizing effect of paclitaxel was tested in vitro using the human U373MG and rat 9L glioma cell lines. Cell cycle arrest in response to paclitaxel exposure was quantified by flow cytometry. Cells were subsequently irradiated, and toxicity was measured using the clonogenic assay. In vivo studies were performed in Fischer 344 rats implanted with intracranial 9L gliosarcoma. Rats were treated with control polymer implants, paclitaxel controlled-release polymers, radiotherapy, or a combination of the 2 treatments. The study end point was survival.

RESULTS

Flow cytometry demonstrated G2-M arrest in both U373MG and 9L cells following 6-12 hours of paclitaxel exposure. The order in which the combination treatment was administered was significant. Exposure to radiation treatment (XRT) during the 6-12 hours after paclitaxel treatment resulted in a synergistic reduction in colony formation. This effect was greater than the effect from either treatment alone and was also greater than the effect of radiation exposure followed by paclitaxel. Rats bearing 9L gliosarcoma tumors treated with paclitaxel polymer administration followed by single-fraction radiotherapy demonstrated a synergistic improvement in survival compared with any other treatment, including radiotherapy followed by paclitaxel treatment. Median survival for control animals was 13 days; for those treated with paclitaxel alone, 21 days; for those treated with XRT alone, 21 days; for those treated with XRT followed by paclitaxel, 45 days; and for those treated with paclitaxel followed by XRT, more than 150 days (p < 0.0001).

CONCLUSIONS

These results indicate that paclitaxel is an effective radiosensitizer for malignant gliomas because it renders glioma cells more sensitive to ionizing radiation by causing G2-M arrest, and induces a synergistic response to chemoradiotherapy.

When gross total resection of a glioblastoma is possible, how much resection should be achieved?

OBJECTIVE

The efficacy of extensive resection on prolonging survival for patients with glioblastoma (GBM) is controversial because prior studies have included tumors with dissimilar resection capabilities. The true isolated effect of increasing resection on survival for GBM therefore remains unclear.

METHODS

Adult patients who underwent surgery of an intracranial newly diagnosed GBM at an academic tertiary-care institution from 2007 to 2011 were reviewed. Preoperative images were reviewed by 3 neurosurgeons independently. Tumors considered amenable to gross total resection based on preoperative imaging by all neurosurgeons were included. Multivariate proportional hazards regression analysis was used to identify if an association existed between residual volume (RV) and extent of resection (EOR) with survival.

RESULTS

Of the 292 patients with newly diagnosed GBM, 84 (29%) were amenable to gross total resection. The median (interquartile range) pre and postoperative tumor volumes were 27 (13.8-54.4) and 0.9 (0-2.7) cm(3), respectively. The mean percent resection was 91.7% ± 1.3%. In multivariate analysis, after controlling for age, functional status, and adjuvant therapies, RV (hazards ratio [HR] [95% confidence interval (CI)] = 1.114 [1.033-1.193], P = 0.006) and EOR (HR [95% CI] = 0.959 [0.934-0.985], P = 0.003) were each independently associated with survival. The RV and EOR with the greatest reduction in the risk of death was <2 cm(3) and >95%, respectively. Likewise, RV (HR [95% CI] = 1.085 [1.010-1.178], P = 0.01) and EOR (HR [95% CI] = 0.962 [0.930-0.998], P = 0.04) each remained independently associated with recurrence.

CONCLUSION

This is the first study to evaluate RV and EOR in a more uniform population of patients with tumors of similar surgical capabilities. This study shows that achieving a decreased RV and/or an increased EOR is independently associated with survival and recurrence in those patients with tumors with similar resection capacities.

Evaluation of post-operative complications associated with repeat resection and BCNU wafer implantation in recurrent glioblastoma

BACKGROUND

Patients with glioblastoma treated with BCNU wafer implantation for recurrence frequently receive frontline chemoradiotherapy with temozolomide as part of the Stupp protocol. A retrospective investigation was conducted of surgical complications in a cohort of these patients treated at a single institution.

METHODS

We searched our institutional database for patients treated between January 2006 and October 2012 who had recurrent glioblastoma previously treated with open surgery followed by the Stupp protocol and then underwent repeat resection with or without BCNU wafers for recurrent disease. Rates of select post-operative complications within 3 months of surgery were estimated.

RESULTS

We identified 95 patients with glioblastoma who underwent resection followed by the Stupp protocol as frontline treatment. At disease recurrence (first and second recurrence), 63 patients underwent repeat resection with BCNU wafer implantation and 32 without implantation. Generally, BCNU wafer use was associated with minor to moderate increases in rates of select complications versus non-implantation-wound healing abnormalities (14.2 vs. 6.2 %), cerebrospinal fluid leak (7.9 vs. 3.1 %), hydrocephalus requiring ventriculoperitoneal shunt (6.3 vs. 9.3 %), chemical meningitis (3.1 vs. 0 %), cerebral infections (3.1 vs. 0 %), cyst formation (3.1 vs. 3.1 %), cerebral edema (4.7 vs. 0 %), and empyema formations (1.5 vs. 0 %). Performance status was well maintained post-operatively in both groups. Median progression-free survival from the time of first recurrence was 6.0 and 5.0 months, respectively.

CONCLUSIONS

The use of the Stupp protocol as frontline therapy in patients with glioblastoma does not preclude the use of BCNU wafers at the time of progression.

Efficacy of local polymer-based and systemic delivery of the anti-glutamatergic agents riluzole and memantine in rat glioma models

OBJECT

The poor outcome of malignant gliomas is largely due to local invasiveness. Previous studies suggest that gliomas secrete excess glutamate and destroy surrounding normal peritumoral brain by means of excitotoxic mechanisms. In this study the authors assessed the effect on survival of 2 glutamate modulators (riluzole and memantine) in rodent glioma models.

METHODS

In an in vitro growth inhibition assay, F98 and 9L cells were exposed to riluzole and memantine. Mouse cerebellar organotypic cultures were implanted with F98 glioma cells and treated with radiation, radiation + riluzole, or vehicle and assessed for tumor growth. Safety and tolerability of intracranially implanted riluzole and memantine CPP:SA polymers were tested in F344 rats. The efficacy of these drugs was tested against the 9L model and riluzole was further tested with and without radiation therapy (RT).

RESULTS

In vitro assays showed effective growth inhibition of both drugs on F98 and 9L cell lines. F98 organotypic cultures showed reduced growth of tumors treated with radiation and riluzole in comparison with untreated cultures or cultures treated with radiation or riluzole alone. Three separate efficacy experiments all showed that localized delivery of riluzole or memantine is efficacious against the 9L gliosarcoma tumor in vivo. Systemic riluzole monotherapy was ineffective; however, riluzole given with RT resulted in improved survival.

CONCLUSIONS

Riluzole and memantine can be safely and effectively delivered intracranially via polymer in rat glioma models. Both drugs demonstrate efficacy against the 9L gliosarcoma and F98 glioma in vitro and in vivo. Although systemic riluzole proved ineffective in increasing survival, riluzole acted synergistically with radiation and increased survival compared with RT or riluzole alone.

Chemotherapy for malignant glioma

Malignant gliomas comprise a small percentage of all cancers, but continue to cause disproportionate levels of morbidity and mortality. Despite decades of intensive effort from many disciplines--surgery, radiation oncology and medicine--they remain refractory to cure and, in most cases, even to prolonged treatment response. Comprehensive multidisciplinary treatment is well recognized as the optimal approach. While continued advances and refinement in both surgical and radiotherapy-based techniques are certain, medical therapies are expanding at a much more rapid rate. This is due, in large part, to an understanding of the molecular events that underlie cancer pathogenesis and improved laboratory techniques to manufacture and study molecules that influence this process. This review will focus on medical therapies in the treatment of malignant glioma, never losing sight of their place as one of several therapeutic modalities used to confront brain cancer.

Treatment of adults with recurrent malignant glioma

Virtually all malignant gliomas recur. Treatment options at recurrence have relied upon surgical intervention, radiation therapy or cytotoxic chemotherapy. Unfortunately, none are associated with significant improvements in survival. Advances in treatment options at recurrence have been dependent upon the combination of surgical resection, focal radiation and chemotherapy. Despite aggressive interventions, few patients have meaningful improvements. Current research focuses on novel targeted molecular therapy that will hopeful be able to take advantage of advances in our understanding of the biology of glial neoplasms.

New treatment strategies for malignant gliomas

Malignant gliomas are the most prevalent type of primary brain tumor in adults. Despite progress in brain tumor therapy, the prognosis of malignant glioma patients remains dismal. The median survival of patients with glioblastoma multiforme, the most common grade of malignant glioma, is 10-12 months. Conventional therapy of surgery, radiation and chemotherapy is largely palliative. Essentially, tumor recurrence is inevitable. Salvage treatments upon recurrence are palliative at best and rarely provide significant survival benefit. Therapies targeting the underlying molecular pathogenesis of brain tumors are urgently required. Common genetic abnormalities in malignant glioma specimens are associated with aberrant activation or suppression of cellular signal transduction pathways and resistance to radiation and chemotherapy. Several low molecular weight signal transduction inhibitors have been examined in preclinical and clinical malignant glioma trials. The efficacy of these agents as monotherapies has been modest, at best; however, small subsets of patients who harbor specific genetic changes in their tumors may display favorable clinical responses to defined small molecule inhibitors. Multitargeted kinase inhibitors or combinations of agents targeting different mitogenic pathways may overcome the resistance of tumors to single-agent targeted therapies. Well designed studies of small molecule kinase inhibitors will include assessment of safety, drug delivery, target inhibition and correlative biomarkers to define mechanisms of response or resistance to these agents. Predictive biomarkers will enrich for patients most likely to respond in future clinical trials. Additional clinical studies will combine novel targeted therapies with radiation, chemotherapies and immunotherapies.

Advances in strategies to improve drug delivery to brain tumors

Brain tumors remain a significant health problem. Advances in the biology of the blood-brain barrier are improving the ability of researchers to target therapeutic peptides, small molecules and other drugs to brain tumors. Simple methods to improve blood-brain barrier penetration include chemical modification, glycosylation and pegylation. Drug-delivery vehicles, such as nanoparticles and liposomes, are also under study. Targeting vectors include natural ligands (e.g., epidermal growth factor) or monoclonal antibodies to receptors (e.g., transferrin or insulin). Other vector-mediated delivery approaches involve the conjugation of a therapeutic peptide or protein with a targeting molecule that can induce transcytosis across blood-brain barrier endothelial cells. The most commonly used vectors are peptidomimetic antibodies to endothelial receptors, such as the transferrin and insulin receptors.

Surgical management of high-grade gliomas

High-grade gliomas, in particular anaplastic astrocytoma and glioblastoma multiforme, represent two of the most devastating forms of brain cancer. In spite of the poor prognosis, new treatments and emerging therapies are making an impact on this disease. This review discusses the role of the surgical management of high-grade gliomas and provides an overview of the currently available therapies which depend on surgical intervention. At the same time, cutting-edge clinical trials for patients with malignant brain tumors are reviewed to provide further insights into potential future therapies.

Drug-releasing implants: current progress, challenges and perspectives

This review presents the different types and concepts of drug-releasing implants using new nanomaterials and nanotechnology-based devices.

Rindopepimut: a promising immunotherapeutic for the treatment of glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common and aggressive glial cell-derived primary tumor. Current standard of care for patients with GBM includes maximal tumor resection plus adjuvant radiotherapy and temozolomide chemotherapy, increasing median overall survival to a mere 15 months from diagnosis. Because these therapies are inherently nonspecific, there is an increased likelihood of off-target and incomplete effects; therefore, targeted modalities are required for enhanced safety and efficacy. Rindopepimut is emerging as a safe and potentially effective drug for the treatment of GBM. Rindopepimut consists of a 14-mer peptide that spans the length of EGF receptor variant III, a mutant variant of EGF receptor found on approximately 30% of primary GBM, conjugated to the carrier protein keyhole limpet hemocyanin. Vaccination with rindopepimut has been shown to specifically eliminate cells expressing EGF receptor variant III. Phase II clinical trials have suggested that vaccination of newly diagnosed GBM patients with rindopepimut plus adjuvant granulocyte-macrophage colony-stimulating factor results in prolonged progression-free and overall survival with minimal toxicity. This review will outline the development of rindopepimut, as well as the current status of this vaccine.

Local delivery of angiogenesis-inhibitor minocycline combined with radiotherapy and oral temozolomide chemotherapy in 9L glioma

OBJECT

Over the past several years, there has been increasing interest in combining angiogenesis inhibitors with radiotherapy and temozolomide chemotherapy in the treatment of glioblastoma. Although the US FDA approved bevacizumab for the treatment of glioblastoma in 2009, the European Medicines Agency rejected its use due to its questionable impact on patient survival. One factor contributing to the failure of angiogenesis inhibitors to increase overall patient survival may be their inability to cross the blood-brain barrier. Here the authors examined in a 9L glioma model whether intracranial polymer-based delivery of the angiogenesis inhibitor minocycline potentiates the effects of both radiotherapy and temozolomide chemotherapy in increasing median survival. The authors also investigated whether the relative timing of minocycline polymer implantation with respect to radiotherapy affects the efficacy of radiotherapy.

METHODS

Minocycline was incorporated into the biodegradable polymer polyanhydride poly(1,3-bis-[p-carboxyphenoxy propane]-co-[sebacic anhydride]) (CPP:SA) at a ratio of 50:50 by weight. Female Fischer 344 rats were implanted with 9L glioma on Day 0. The minocycline polymer was then implanted on either Day 3 or Day 5 posttumor implantation. Cohorts of rats were exposed to 20 Gy focal radiation on Day 5 or were administered oral temozolomide (50 mg/kg daily) on Days 5-9.

RESULTS

Both minocycline polymer implantations on Days 3 and 5 increased survival from 14 days to 19 days (p < 0.001 vs control). Treatment with a combination of both minocycline polymer and radiotherapy on Day 5 resulted in a 139% increase in median survival compared with treatment with radiotherapy alone (p < 0.005). There was not a statistically significant difference in median survival between the group that received minocycline implanted on the same day as radiotherapy and the group that received minocycline polymer 2 days prior to radiotherapy. Lastly, treatment with a combination of minocycline polymer with oral temozolomide resulted in a 38% extension of median survival compared with treatment of oral temozolomide alone (p < 0.001).

CONCLUSIONS

These results show that minocycline delivered locally potentiates the effects of both radiotherapy and oral temozolomide in increasing median survival in a rodent glioma model. More generally, these results suggest that traditional therapy in combination with local, as opposed to systemic, delivery of angiogenesis inhibitors may be able to increase median survival for patients with glioblastoma.

Heat-shock protein peptide complex-96 vaccination for recurrent glioblastoma: a phase II, single-arm trial

BACKGROUND

Outcomes for patients with recurrent glioblastoma multiforme (GBM) are poor and may be improved by immunotherapy. We investigated the safety and efficacy of an autologous heat-shock protein peptide complex-96 (HSPPC-96) vaccine for patients with recurrent GBM.

METHODS

In this open-label, single-arm, phase II study, adult patients with surgically resectable recurrent GBM were given vaccine after gross total resection. The primary endpoint was overall survival at 6 months. Secondary endpoints included overall survival, progression-free survival, safety, and immune profiling. Outcome analyses were performed in the intention-to-treat and efficacy populations.

RESULTS

Between October 3, 2007 and October 24, 2011, 41 patients underwent gross total resection of recurrent GBM and received a median of 6 doses of HSPPC-96 vaccine. Following treatment, 90.2% of patients were alive at 6 months (95% confidence interval [CI]: 75.9-96.8) and 29.3% were alive at 12 months (95% CI: 16.6-45.7). Median overall survival was 42.6 weeks (95% CI: 34.7-50.5). Twenty-seven (66%) patients were lymphopenic prior to therapy, and patients with lymphocyte counts below the cohort median demonstrated decreased overall survival (hazard ratio: 4.0; 95% CI: 1.4-11.8; P = .012). There were no treatment-related deaths. There were 37 serious (grades 3-5) adverse events reported, with 17 attributable to surgical resection and a single grade 3 constitutional event related to the vaccine.

CONCLUSION

The HSPPC-96 vaccine is safe and warrants further study of efficacy for the treatment of recurrent GBM. Significant pretreatment lymphopenia may impact the outcomes of immunotherapy and deserves additional investigation.

Delayed post-operative haemorrhage after carmustine wafer implantation: a case series from two UK centres

OBJECT

Significant haemorrhage following intracranial tumour resection may occur in 1-2% of cases and the majority occur within the first few hours post-operatively. Implantation of carmustine wafers has been associated with increased operative site complications in some series, but post-operative haematoma is not routinely reported. We analyzed the characteristics of post-operative haemorrhage after carmustine wafer insertion.

METHODS

We performed a retrospective audit of surgical site haematoma after tumour resection and insertion of carmustine wafers in two neurosurgical units in the UK (University Hospital of North Staffordshire, Stoke-on-Trent, March 2003 - July 2012; Wessex Neurological Centre, Southampton, October 2005 - January 2013).

RESULTS

During the specified time periods, carmustine wafers were inserted in 181 operations in 177 patients. We identified acute operative site haematomas after carmustine wafer insertion in 8 (4.4%) patients. All presented in a delayed fashion on or after Day 2 post-operatively. In contrast, acute operative site haematoma was present in 4/491 (0.81%) of patients who underwent resection without gliadel wafer insertion.

CONCLUSIONS

In contrast to the expected timing of bleeding following intracranial tumour resection, all carmustine wafer patients who experienced haemorrhage presented in a delayed fashion on or after Day 2 post-operatively. The causative factors for universally delayed post-operative haematoma after carmustine wafer insertion are unclear and further studies are required to characterize this phenomenon.

A multicenter phase I/II study of the BCNU implant (Gliadel(®) Wafer) for Japanese patients with malignant gliomas

Carmustine (BCNU) implants (Gliadel^® Wafer, Eisai Inc., New Jersey, USA) for the treatment of malignant gliomas (MGs) were shown to enhance overall survival in comparison to placebo in controlled clinical trials in the United States and Europe. A prospective, multicenter phase I/II study involving Japanese patients with MGs was performed to evaluate the efficacy, safety, and pharmacokinetics of BCNU implants. The study enrolled 16 patients with newly diagnosed MGs and 8 patients with recurrent MGs. After the insertion of BCNU implants (8 sheets maximum, 61.6 mg BCNU) into the removal cavity, various chemotherapies (including temozolomide) and radiotherapies were applied. After placement, overall and progression-free survival rates and whole blood BCNU levels were evaluated. In patients with newly diagnosed MGs, the overall survival rates at 12 months and 24 months were 100.0% and 68.8%, and the progression-free survival rate at 12 months was 62.5%. In patients with recurrent MGs, the progression-free survival rate at 6 months was 37.5%. There were no grade 4 or higher adverse events noted due to BCNU implants, and grade 3 events were observed in 5 of 24 patients (20.8%). Whole blood BCNU levels reached a peak of 19.4 ng/mL approximately 3 hours after insertion, which was lower than 1/600 of the peak BCNU level recorded after intravenous injections. These levels decreased to less than the detection limit (2.00 ng/mL) after 24 hours. The results of this study involving Japanese patients are comparable to those of previous studies in the United States and Europe.

Establishing percent resection and residual volume thresholds affecting survival and recurrence for patients with newly diagnosed intracranial glioblastoma

INTRODUCTION

Surgery is first-line therapy for glioblastoma, and there is evidence that gross total resection is associated with improved survival. Gross total resection, however, is not always possible, and relationships among extent (percent) of resection (EOR), residual volume (RV), and survival are unknown. The goals were to evaluate whether there is an association between EOR and RV with survival and recurrence and to establish minimum EOR and maximum RV thresholds.

METHODS

Adult patients who underwent primary glioblastoma surgery from 2007 to 2011 were retrospectively reviewed. Three-dimensional volumetric tumor measurements were made. Multivariate proportional hazards regression analysis was used to evaluate the relationship between EOR and RV with survival and recurrence.

RESULTS

Of 259 patients, 203 (78%) died and 156 (60%) had tumor recurrence. The median survival and progression-free survival were 13.4 and 8.9 months, respectively. The median (interquartile range) pre- and postoperative tumor volumes were 32.2 (14.0-56.3) and 2.1 (0.0-7.9) cm(3), respectively. EOR was independently associated with survival (hazard ratio [HR], 0.995; 95% confidence interval [CI]: 0.990-0.998; P = .008) and recurrence (HR [95% CI], 0.992 [0.983-0.998], P = .005). The minimum EOR threshold for survival (P = .0006) and recurrence (P = .005) was 70%. RV was also associated with survival (HR [95% CI], 1.019 [1.006-1.030], P = .004) and recurrence (HR [95% CI], 1.024 [1.001-1.044], P = .03). The maximum RV threshold for survival (P = .01) and recurrence (P = .01) was 5 cm(3).

CONCLUSION

This study shows for the first time that both EOR and RV are significantly associated with survival and recurrence, where the thresholds are 70% and 5 cm(3), respectively. These findings may help guide surgical and adjuvant therapies aimed at optimizing outcomes for glioblastoma patients.

Accelerated hazards model based on parametric families generalized with Bernstein polynomials

A transformed Bernstein polynomial that is centered at standard parametric families, such as Weibull or log-logistic, is proposed for use in the accelerated hazards model. This class provides a convenient way towards creating a Bayesian nonparametric prior for smooth densities, blending the merits of parametric and nonparametric methods, that is amenable to standard estimation approaches. For example optimization methods in SAS or R can yield the posterior mode and asymptotic covariance matrix. This novel nonparametric prior is employed in the accelerated hazards model, which is further generalized to time-dependent covariates. The proposed approach fares considerably better than previous approaches in simulations; data on the effectiveness of biodegradable carmustine polymers on recurrent brain malignant gliomas is investigated.

Risk factors and outcomes associated with surgical site infections after craniotomy or craniectomy

OBJECT

Many studies that have evaluated surgical site infections (SSIs) after craniotomy or craniectomy (CRANI) did not use robust methods to assess risk factors for SSIs or outcomes associated with SSIs. The authors conducted the current study to identify risk factors for SSIs after CRANI procedures and to evaluate outcomes attributed to SSIs.

METHODS

The authors performed a nested case-control study of patients undergoing CRANI procedures between 2006 and 2010 at the University of Iowa Hospitals and Clinics. They identified 104 patients with SSIs and selected 312 controls. They collected data from medical records and used multivariate analyses to identify risk factors and outcomes associated with SSIs.

RESULTS

Thirty-two percent of SSIs were caused by Staphylococcus aureus, 88% were deep incisional or organ space infections, and 70% were identified after discharge. Preoperative length of stay (LOS) ≥ 1 day was the only significant patient-related factor in the preoperative model (OR 2.1 [95% CI 1.2-3.4]) and in the overall model (OR 1.9 [95% CI 1.1-3.3]). Procedure-related risk factors that were significant in the overall model included Gliadel wafer use (OR 6.7 [95% CI 2.5-18.2]) and postoperative CSF leak (OR 3.5 [95% CI 1.4-8.5]). The preoperative SSI risk index, including body mass index, previous brain operation, chemotherapy on admission, preoperative LOS, procedure reason, and preoperative glucose level, had better predictive efficacy (c-statistic = 0.664) than the National Healthcare Safety Network risk index (c-statistic = 0.547; p = 0.004). Surgical site infections were associated with increased LOS during the initial hospitalizations (average increase of 50%) or readmissions (average increase of 100%) and with an increased risk of readmissions (OR 7.7 [95% CI 4.0-14.9]), reoperations (OR 36 [95% CI 14.9-87]), and death (OR 3.4 [95% CI 1.5-7.4]).

CONCLUSIONS

Surgeons were able to prospectively assess a patient's risk of SSI based on preoperative risk factors and they could modify some processes of care to lower the risk of SSI. Surgical site infections substantially worsened patients' outcomes. Preventing SSIs after CRANI could improve patient outcomes and decrease health care utilization.

Fibrin-binding, peptide amphiphile micelles for targeting glioblastoma

Glioblastoma-targeted drug delivery systems facilitate efficient delivery of chemotherapeutic agents to malignant gliomas, while minimizing systemic toxicity and side effects. Taking advantage of the fibrin deposition that is characteristic of tumors, we constructed spherical, Cy7-labeled, targeting micelles to glioblastoma through the addition of the fibrin-binding pentapeptide, cysteine–arginine–glutamic acid–lysine–alanine, or CREKA. Conjugation of the CREKA peptide to Cy7-micelles increased the average particle size and zeta potential. Upon intravenous administration to GL261 glioma bearing mice, Cy7-micelles passively accumulated at the brain tumor site via the enhanced permeability and retention (EPR) effect, and Cy7-CREKA-micelles displayed enhanced tumor homing via active targeting as early as 1 h after administration, as confirmed via in vivo and ex vivo imaging and immunohistochemistry. Biodistribution of micelles showed an accumulation within the liver and kidneys, leading to micelle elimination via renal clearance and the reticuloendothelial system (RES). Histological evaluation showed no signs of cytotoxicity or tissue damage, confirming the safety and utility of this nanoparticle system for delivery to glioblastoma. Our findings offer strong evidence for the glioblastoma-targeting potential of CREKA-micelles and provide the foundation for CREKA-mediated, targeted therapy of glioma.

Modeling mass transfer from carmustine-loaded polymeric implants for malignant gliomas

Significant advances in the encapsulation and release of drugs from degradable polymers have led to the Food and Drug Administration approval of Gliadel wafers for controlled local delivery of the chemotherapeutic drug carmustine to high-grade gliomas following surgical resection. Due to the localized nature of the delivery method, no pharmacokinetic measurements have been taken in humans. Rather, pharmacokinetic studies in animals and associated modeling have indicated the capability of carmustine to be delivered in high concentrations within millimeters from the implant site over approximately 5 days. Mathematical models have indicated that diffusion has a primary role in transport, which may be complemented by enhanced fluid convection from postsurgical edema in the initial 3 days following implantation. Carmustine's penetration distance is also presumably limited by its lipophilicity and permeability in the capillaries. This review discusses the mathematical models that have been used to predict the release and distribution of carmustine from a polymeric implant. These models provide a theoretical framework for greater understanding of systems for localized drug delivery while highlighting factors that should be considered in clinical applications. In effect, Gliadel wafers and similar drug delivery implants can be optimized with reduction in required time and resources with such a quantitative and integrative approach.

Preservation of neurocognitive function and local control of 1 to 3 brain metastases treated with surgery and carmustine wafers

Background

Neurosurgical resection and whole-brain radiation therapy (WBRT) are accepted treatments for single and oligometastatic cancer to the brain. To avoid the decline in neurocognitive function (NCF) linked to WBRT, the authors conducted a prospective, multicenter, phase 2 study to determine whether surgery and carmustine wafers (CW), while deferring WBRT, could preserve NCF and achieve local control (LC).

Methods

NCF and LC were measured in 59 patients who underwent resection and received CW for a single (83%) or dominant (oligometastatic, 2 to 3 lesions) metastasis and received stereotactic radiosurgery (SRS) for tiny nodules not treated with resection plus CW. Preservation of NCF was defined as an improvement or a decline ≤1 standard deviation from baseline in 3 domains: memory, executive function, and fine motor skills, evaluated at 2-month intervals.

Results

Significant improvements in executive function and memory occurred throughout the 1-year follow-up. Preservation or improvement of NCF occurred in all 3 domains for the majority of patients at each of the 2-month intervals. NCF declined in only 1 patient. The chemowafers were well tolerated, and serious adverse events were reversible. There was local recurrence in 28% of the patients at 1-year follow-up.

Conclusions

Patients with brain metastases had improvements in their cognitive trajectory, especially memory and executive function, after treatment with resection plus CW. The rate of LC (78%) was comparable to historic rates of surgery with WBRT and superior to reports of WBRT alone. For patients who undergo resection for symptomatic or large-volume metastasis or for tissue diagnosis, the addition of CW can be considered as an option.

Multi-institutional validation of a preoperative scoring system which predicts survival for patients with glioblastoma

Glioblastoma is the most common and aggressive type of primary brain tumor in adults. Average survival is approximately 1 year, but individual survival is heterogeneous. Using a single institutional experience, we have previously identified preoperative factors associated with survival and devised a prognostic scoring system based on these factors. The aims of the present study are to validate these preoperative factors and verify the efficacy of this scoring system using a multi-institutional cohort. Of the 334 patients in this study from three different institutions, the preoperative factors found to be negatively associated with survival in a Cox analysis were age >60 years (p<0.0001), Karnofsky Performance Scale score ≤80 (p=0.03), motor deficit (p=0.02), language deficit (p=0.04), and periventricular tumor location (p=0.04). Patients possessing 0-1, 2, 3, and 4-5 of these variables were assigned a preoperative grade of 1, 2, 3, and 4, respectively. Patients with a preoperative grade of 1, 2, 3, and 4 had a median survival of 17.9, 12.3, 10, and 7.5 months, respectively. Survival of each of these grades was statistically significant (p<0.05) in log-rank analysis. This grading system, based only on preoperative variables, may provide patients and physicians with prognostic information that may guide medical and surgical therapy before any intervention is pursued.

Highly penetrative, drug-loaded nanocarriers improve treatment of glioblastoma

Current therapy for glioblastoma multiforme is insufficient, with nearly universal recurrence. Available drug therapies are unsuccessful because they fail to penetrate through the region of the brain containing tumor cells and they fail to kill the cells most responsible for tumor development and therapy resistance, brain cancer stem cells (BCSCs). To address these challenges, we combined two major advances in technology: (i) brain-penetrating polymeric nanoparticles that can be loaded with drugs and are optimized for intracranial convection-enhanced delivery and (ii) repurposed compounds, previously used in Food and Drug Administration-approved products, which were identified through library screening to target BCSCs. Using fluorescence imaging and positron emission tomography, we demonstrate that brain-penetrating nanoparticles can be delivered to large intracranial volumes in both rats and pigs. We identified several agents (from Food and Drug Administration-approved products) that potently inhibit proliferation and self-renewal of BCSCs. When loaded into brain-penetrating nanoparticles and administered by convection-enhanced delivery, one of these agents, dithiazanine iodide, significantly increased survival in rats bearing BCSC-derived xenografts. This unique approach to controlled delivery in the brain should have a significant impact on treatment of glioblastoma multiforme and suggests previously undescribed routes for drug and gene delivery to treat other diseases of the central nervous system.

Biomaterials and biotechnology: from the discovery of the first angiogenesis inhibitors to the development of controlled drug delivery systems and the foundation of tissue engineering

This paper describes the discovery of the first inhibitors of angiogenesis; the discoveries that led to the development of the first biocompatible controlled release systems for macromolecules, and findings that helped to create the field of tissue engineering. In addition, new paradigms for creating biomaterials, early work on nanotechnology in medicine and intelligent drug delivery systems are discussed.

Convection-enhanced delivery: from mechanisms to clinical drug delivery for diseases of the central nervous system

The evolution of cancer chemotherapy has been a major advance in medical science in the late 20th century. However, patients with malignant gliomas have not benefitted much. The blood-brain barrier (BBB), which always hinders the entry of therapeutic agents into the central nervous system (CNS), may at least partly be responsible. Convection-enhanced delivery (CED), a method for distributing large and small molecular weight compounds bypassing the BBB, enables robust distribution of the infused molecules at the site of infusion. CED is promising as an effective treatment not only for malignant gliomas but also for multiple CNS disorders because this method can effectively distribute multiple molecules that are potentially effective against different diseases. Although the method is quite simple, several problems require solution in developing novel CED-based strategies, including what, where, when, and how to infuse. This review discusses basic considerations when developing CED-based strategies for CNS diseases, focusing mainly on brain tumors.

Current status of local therapy in malignant gliomas--a clinical review of three selected approaches

Malignant gliomas are the most frequently occurring, devastating primary brain tumors, and are coupled with a poor survival rate. Despite the fact that complete neurosurgical resection of these tumors is impossible in consideration of their infiltrating nature, surgical resection followed by adjuvant therapeutics, including radiation therapy and chemotherapy, is still the current standard therapy. Systemic chemotherapy is restricted by the blood-brain barrier, while methods of local delivery, such as with drug-impregnated wafers, convection-enhanced drug delivery, or direct perilesional injections, present attractive ways to circumvent these barriers. These methods are promising ways for direct delivery of either standard chemotherapeutic or new anti-cancer agents. Several clinical trials showed controversial results relating to the influence of a local delivery of chemotherapy on the survival of patients with both recurrent and newly diagnosed malignant gliomas. Our article will review the development of the drug-impregnated release, as well as convection-enhanced delivery and the direct injection into brain tissue, which has been used predominantly in gene-therapy trials. Further, it will focus on the use of convection-enhanced delivery in the treatment of patients with malignant gliomas, placing special emphasis on potential shortcomings in past clinical trials. Although there is a strong need for new or additional therapeutic strategies in the treatment of malignant gliomas, and although local delivery of chemotherapy in those tumors might be a powerful tool, local therapy is used only sporadically nowadays. Thus, we have to learn from our mistakes in the past and we strongly encourage future developments in this field.

Update on bevacizumab and other angiogenesis inhibitors for brain cancer

INTRODUCTION

Primary and metastatic brain tumors remain a major challenge. The most common primary adult malignant brain tumor, glioblastoma (GBM), confers a dismal prognosis as does the development of CNS metastases for most systemic malignancies. Anti-angiogenic therapy has been a major clinical research focus in neuro-oncology over the past 5 years.

AREAS COVERED

Culmination of this work includes US FDA accelerated approval of bevacizumab for recurrent GBM and the completion of two placebo-controlled Phase III studies of bevacizumab for newly diagnosed GBM. A multitude of anti-angiogenics are in evaluation for neuro-oncology patients but none has thus far surpassed the therapeutic benefit of bevacizumab.

EXPERT OPINION

These agents demonstrate adequate safety and the majority of GBM patients derive benefit. Furthermore, their anti-permeability effect can substantially decrease tumor-associated edema leading to stable or improved neurologic function and quality of life. In particular, anti-angiogenics significantly prolong progression-free survival - a noteworthy achievement in the context of infiltrative and destructive brain tumors like GBM; however, in a manner analogous to other cancers, their impact on overall survival for GBM patients is modest at best. Despite substantial clinical research efforts, many fundamental questions regarding anti-angiogenic agents in brain tumor patients remain unanswered.

MGMT promoter methylation status and prognosis of patients with primary or recurrent glioblastoma treated with carmustine wafers

The prognostic role of O(6)-methylguanine-DNA methyltransferase (MGMT) promoter methylation in glioblastoma patients treated with carmustine (BCNU) wafer implantation is unclear. Here, we report on a retrospective study of 47 patients with either newly diagnosed (30 patients) or recurrent (17 patients) glioblastoma (WHO grade IV) treated with BCNU (bis-chloroethylnitrosourea) wafers. Thirteen of the newly diagnosed patients received local BCNU and irradiation only (first-line BCNU), while 17 patients additionally received concomitant and adjuvant temozolomide (TMZ) radiochemotherapy (first-line BCNU + TMZ). Of the 17 patients treated for recurrent glioblastoma (second-line BCNU), 16 had received radiotherapy with concomitant and adjuvant TMZ as an initial treatment. Median overall survival (OS) did not significantly differ between 19 patients with MGMT promoter methylated tumors when compared to 28 patients with unmethylated tumors (18.9 vs 15.0 months; p = 0.1054). In the first-line BCNU + TMZ group, MGMT promoter methylation was associated with longer OS (21.0 vs 11.1 months, p = 0.0127), while no significant survival differences were detected in the other two subgroups. Progression-free survival did not significantly differ between patients with and without MGMT promoter methylated tumors in the entire patient cohort or any of the three subgroups. The first-line BCNU + TMZ group showed no significant difference in OS when compared to the first-line BCNU group (18.9 vs 14.7 months), but tended to have more therapy-related adverse effects (53% vs 24%, p = 0.105). In summary, MGMT promoter methylation showed a non-significant trend toward longer survival in our patient cohort. The combination of TMZ radiochemotherapy with local delivery of BCNU did not provide a significant survival benefit compared to local BCNU alone, but was associated with a higher rate of adverse effects. Owing to the small number of patients investigated, however, these findings would need to be corroborated in larger patient cohorts.

Gliadel for brain metastasis

With therapies for systemic malignancy improving, life expectancy for cancer patients is becoming increasingly dependent on control of brain metastatic disease. Despite improvements in surgical and radiotherapy modalities for control of brain metastasis, the prognosis for patients with brain metastases is poor. The development of controlled release polymers has lead to novel new therapies for malignant brain tumors consisting of direct surgical delivery of chemotherapy agents to the tumor bed and sustained chemotherapy release over a prolonged period of time. Although there is a large body of literature in support of BCNU polymer wafer for primary brain malignancy and experimental brain metastases, clinical studies evaluating the BCNU polymer wafer for brain metastatic disease are relatively sparse. In this review, we discuss the role of the BCNU polymer wafer for brain metastasis focusing specifically on rationale for use of locally delivered sustained release polymers, history of the BCNU polymer wafer, and emerging studies examining the role of the BCNU polymer wafer for metastatic brain tumors.

Current trends in glioblastoma multiforme treatment: radiation therapy and immune checkpoint inhibitors

Glioblastoma multiforme (GBM) is the most common primary brain cancer. Even with aggressive combination therapy, the median life expectancy for patients with GBM remains approximately 14 months. In order to improve the outcomes of patients with GBM, the development of newer treatments is critical. The concept of using the immune system as a therapeutic option has been suggested for several decades; by harnessing the body's adaptive immune mechanisms, immunotherapy could provide a durable and targeted treatment against cancer. However, many cancers, including GBM, have developed mechanisms that protect tumor cells from being recognized and eliminated by the immune system. For new immunotherapeutic regimens to be successful, overcoming immunosuppression via immune checkpoint signaling should be taken into consideration.

Management of large aggressive nonfunctional pituitary tumors: experimental medical options when surgery and radiation fail

Pituitary adenomas are generally considered benign tumors; however, a subset of these tumors displays aggressive behavior and are not easily cured. The protocol for nonsurgical treatment of aggressive pituitary lesions is less standardized than that of other central nervous system tumors. Aggressive surgical treatment, radiation, dopamine agonists, antiangiogenic drugs, and other chemotherapeutics all have roles in the treatment of aggressive pituitary tumors. More studies are needed to improve outcomes for patients with aggressive pituitary tumors.

Prolonged survival associated with the use of intraoperative carmustine (Gliadel) in a paediatric patient with recurrent grade III astrocytoma

A 15-year-old female presented with a middle cranial fossa anaplastic astrocytoma that was completely excised. She received local radiotherapy (54 Gy) and oral temozolomide. Five months after therapy, MRI showed local relapse. She underwent resection of the tumour with implantation of seven carmustine-impregnated wafers (Gliadel). She then received six cycles of procarbazine and lomustine therapy. Three years later, she is well and disease free. This case supports the further investigation of Gliadel in children and young people with relapsed high-grade glioma, particularly in the setting of a second complete resection.

Prospective study of carmustine wafers in combination with 6-month metronomic temozolomide and radiation therapy in newly diagnosed glioblastoma: preliminary results

OBJECT

Locoregional chemotherapy with carmustine wafers, positioned at surgery and followed by radiation therapy, has been shown to prolong survival in patients with newly diagnosed glioblastoma, as has concomitant radiochemotherapy with temozolomide. A combination of carmustine wafers with the Stupp treatment regimen has only been investigated in retrospective studies.

METHODS

In a single-institution prospective study, the authors assessed 12-month progression-free survival (PFS), toxicity, and overall survival in patients with glioblastoma treated with surgery, carmustine wafers, radiotherapy, and 6-month metronomic temozolomide chemotherapy. Thirty-five patients with de novo glioblastoma, between the ages of 18 and 70 years, and with Karnofsky Performance Scale scores of at least 70, were included in the study. Patients were followed monthly and assessed using MRI every 2 months.

RESULTS

After a median follow-up of 15 months, the median time to tumor progression was 12.5 months and median survival was 17.8 months. Due to toxicity (mostly hematological), 7 patients had to prematurely stop temozolomide treatment. Twenty-two patients developed Grade 3 CD4(+) lymphocytopenia. Three patients developed oral-esophageal candidiasis, 2 developed pneumonia, and 1 developed a dorsolumbar zoster. Early intracranial hypertension was observed in 1 patient, and 1 was treated empirically for suspected brain abscess. One patient died of Legionella pneumonia soon after repeat surgery.

CONCLUSIONS

Overall, this treatment schedule produced promising results in terms of PFS without a marked increase in toxicities as compared with the Stupp regimen. However, the gain in median survival using this schedule was less clear. Only prospective comparative trials will determine whether these preliminary results will translate into a long-term survival advantage with an acceptable toxicity profile.

Long-term survival of patients with glioblastoma multiforme (GBM)

Long-term survival is an often used, yet poorly defined, concept in the study of glioblastoma multiforme (GBM). This study suggests a method to define a time-point for long-term survival in patients with GBM. Data for this study were obtained from the Surveillance, Epidemiology and End-Results database, which was limited to the most recent data using the period approach. Relative survival measures were used and modelled using piecewise constant hazards to describe the survival profile of long-term survivors of GBM. For patients with GBM, the first quarter of the second year (5th quarter) post-diagnosis is considered to be the peak incidence of mortality with an excess hazard ratio of 7.58 (95% confidence interval=6.54, 8.78) and the risk of death due to GBM decreases to half of its rate at 2.5 years post-diagnosis. The 2.5-year cumulative relative survival (CRS) for all patients is approximately 8%, with a CRS of approximately 2% at 10 years. Using the definition of long-term survival suggested here, the results indicate that long-term survivors are patients who survive at least 2.5 years post-diagnosis. The most likely time period for patients with GBM to die is the 5th quarter post-diagnosis.

Growth pattern of tumor recurrence following bis-chloroethylnitrosourea (BCNU) wafer implantation in malignant glioma

Bis-chloroethylnitrosourea (BCNU; Gliadel, Eisai, Tokyo, Japan) is the only therapeutic agent for local chemotherapy of malignant gliomas approved by the US Food and Drug Administration and the European Medicines Agency. In a small patient cohort, it has previously been shown that glioblastomas recur locally despite treatment with BCNU. This raises concern about local treatment with BCNU as a stand-alone measure. The goal of this study was to analyze the growth pattern of tumor recurrence in a larger patient group: 41 patients were included in this study. Tumor recurrences were morphologically categorized as: local, diffuse, distant or multilocular. Thirty-three of the tumors (80%) that recurred were local or diffuse. These results show that BCNU implantation does not provide lasting local tumor control. Our data support the need to incorporate BCNU in to multimodal therapy schemes. The improved survival rates of patients who receive concomitant local and systemic adjuvant treatment support using local therapy to bridge the therapy-free interval of the initial postoperative phase.

A New Semiparametric Estimation Method for Accelerated Hazards Mixture Cure Model

The semiparametric accelerated hazards mixture cure model provides a useful alternative to analyze survival data with a cure fraction if covariates of interest have a gradual effect on the hazard of uncured patients. However, the application of the model may be hindered by the computational intractability of its estimation method due to non-smooth estimating equations involved. We propose a new semiparametric estimation method based on a smooth estimating equation for the model and demonstrate that the new method makes the parameter estimation more tractable without loss of efficiency. The proposed method is used to fit the model to a SEER breast cancer data set.