Efficient semiparametric estimation in generalized partially linear additive models

유규상,이영경 한국통계학회 2010 Journal of the Korean Statistical Society Vol.39 No.3

In this paper we study semiparametric generalized additive models in which some part of the additive function is linear. We study the semiparametric efficiency under this regression model for the exponential family. We also present an asymptotically efficient estimation procedure based on the generalized profile likelihood approach.

『今昔物語集』 卷十七の地藏說話に關する考察

柳圭相 경희대학교 대학원 일어일문학과 일본학논집간행회 1999 일본학논집 Vol.10 No.-

Comparison of Breast Conserving Surgery Followed by Radiation Therapy with Mastectomy Alone for Pathologic N1 Breast Cancer Patients in the Era of Anthracycline Plus Taxane-Based Chemotherapy: A Multicenter Retrospective Study (KROG 1418)

유규상,박원,유정일,최두호,김연주,신경환,위찬우,김규보,박경란,김용배,안성자,이종훈,김진희,전미선,이형식,김정수,차지혜 대한암학회 2019 Cancer Research and Treatment Vol.51 No.3

Purpose We compared the oncologic outcomes of breast-conserving surgery plus radiation therapy (BCS+RT) and modified radical mastectomy (MRM) under anthracycline plus taxane-based (AT) regimens and investigated the role of adjuvant radiation therapy (RT) in patients with pathologic N1 (pN1) breast cancer treated by mastectomy. Materials and Methods We retrospectively reviewed the medical records of 2,011 patients with pN1 breast cancer who underwent BCS+RT or MRM alone at 12 institutions between January 2006 and December 2010. Two-to-one propensity score matching was performed for balances in variables between the groups. Results The median follow-up duration for the total cohort was 69 months (range, 1 to 114 months). After propensity score matching, 1,074 patients (676 in the BCS+RT group and 398 in the MRM-alone group) were analyzed finally. The overall survival, disease-free survival, locoregional failure-free survival, and regional failure-free survival (RFFS) curves of the BCS+RT group vs. MRM-alone group were not significantly different. The subgroup analysis revealed that in the group with both lymphovascular invasion (LVI) and histologic grade (HG) III, the BCS+RT showed significantly superior RFFS (p=0.008). Lymphedema (p=0.007) and radiation pneumonitis (p=0.031) occurred more frequently in the BCS+RT group than in the MRM-alone group, significantly. Conclusion There are no differences in oncologic outcomes between BCS+RT and MRM-alone groups under the AT chemotherapy regimens for pN1 breast cancer. However, BCS+RT group showed superior RFFS to MRM-alone group in the patients with LVI and HG III. Adjuvant RT might be considerable for pN1 breast cancer patients with LVI and HG III.

Conditional variance estimation via nonparametric generalized additive models

유규상 한국통계학회 2019 Journal of the Korean Statistical Society Vol.48 No.2

Generalized additive models provide a way of circumventing curse of dimension in a wide range of nonparametric regression problem. In this paper, we present a multiplicative model for conditional variance functions where one can apply a generalized additive regression method. This approach extends Fan and Yao (1998) to multivariate cases with a multiplicative structure. In this approach, we use squared residuals instead of using logtransformed squared residuals. This idea gives a smaller variance than Yu (2017) when the variance of squared error is smaller than the variance of log-transformed squared error.We provide estimators based on quasi-likelihood and an iterative algorithm based on smooth backfitting for generalized additive models. We also provide some asymptotic properties of estimators and the convergence of proposed algorithm. A numerical study shows the empirical evidence of the theory.

Prognostic factors in breast cancer with extracranial oligometastases and the appropriate role of radiation therapy

유규상,유정일,박원,허승재,최두호 대한방사선종양학회 2015 Radiation Oncology Journal Vol.33 No.4

Purpose: To identify prognostic factors for disease progression and survival of patients with extracranial oligometastatic breast cancer (EOMBC), and to investigate the role of radiation therapy (RT) for metastatic lesions. Materials and Methods: We retrospectively reviewed the medical records of 50 patients who had been diagnosed with EOMBC following standard treatment for primary breast cancer initially, and received RT for metastatic lesions, with or without other systemic therapy between January 2004 and December 2008. EOMBC was defined as breast cancer with five or less metastases involving any organs except the brain. All patients had bone metastasis (BM) and seven patients had pulmonary, hepatic, or lymph node metastasis. Median RT dose applied to metastatic lesions was 30 Gy (range, 20 to 60 Gy). Results: The 5-year tumor local control (LC) and 3-year distant progression-free survival (DPFS) rate were 66.1% and 36.8%, respectively. High RT dose (≥50 Gy10) was significantly associated with improved LC. The 5-year overall survival (OS) rate was 49%. Positive hormone receptor status, pathologic nodal stage of primary cancer, solitary BM, and whole-lesion RT (WLRT), defined as RT whose field encompassed entire extent of disease, were associated with better survival. On analysis for subgroup of solitary BM, high RT dose was significantly associated with improved LC and DPFS, shorter metastasis-to-RT interval (≤1 month) with improved DPFS, and WLRT with improved DPFS and OS, respectively. Conclusion: High-dose RT in solitary BM status and WLRT have the potential to improve the progression-free survival and OS of patients with EOMBC.

Chronological Analysis of Acute Hematological Outcomes after Proton and Photon Beam Craniospinal Irradiation in Pediatric Brain Tumors

유규상,유정일,조성구,한영이,오윤진,임도훈,남희림,이지원,성기웅,신형진 대한암학회 2022 Cancer Research and Treatment Vol.54 No.3

PurposeThis study aimed to compare the early hematological dynamics and acute toxicities between proton beam craniospinal irradiation (PrCSI) and photon beam craniospinal irradiation (PhCSI) for pediatric brain tumors.Materials and Methods We retrospectively reviewed patients with pediatric brain tumors who received craniospinal irradiation (CSI). The average change in hemoglobin levels (ΔHb_avg), absolute lymphocyte counts (ΔALC_avg), and platelet counts (ΔPLT_avg) from baseline values was evaluated and compared between the PrCSI and PhCSI groups at 1 and 2 weeks after the initiation of CSI, 1 week before and at the end of radiotherapy, and 3-4 weeks after the completion of radiotherapy using t test and mixed-model analysis.Results The PrCSI and PhCSI groups consisted of 36 and 30 patients, respectively. There were no significant differences in ΔHb_avg between the two groups at any timepoint. However, ΔALC_avg and ΔPLT_avg were significantly lower in the PhCSI group than in PrCSI group at every timepoint, demonstrating that PrCSI resulted in a significantly lower rate of decline and better recovery of absolute lymphocyte and platelet counts. The rate of grade 3 acute anemia was significantly lower in the PrCSI group than in in the PhCSI group.Conclusion PrCSI showed a lower rate of decline and better recovery of absolute lymphocyte and platelet counts than PhCSI in the CSI for pediatric brain tumors. Grade 3 acute anemia was significantly less frequent in the PrCSI group than in the PhCSI group. Further large-scale studies are warranted to confirm these results.

Carcinoembryonic Antigen Improves the Performance of Magnetic Resonance Imaging in the Prediction of Pathologic Response after Neoadjuvant Chemoradiation for Patients with Rectal Cancer

유규상,박희철,유정일,최두호,조원경,박영석,박준오,임호영,강원기,이우용,김희철,윤성현,조용범,박윤아,송경두,김석형,하상윤 대한암학회 2020 Cancer Research and Treatment Vol.52 No.2

Purpose The purpose of this study was to investigate the role of carcinoembryonic antigen (CEA) levels in improving the performance of magnetic resonance imaging (MRI) for the prediction of pathologic response after the neoadjuvant chemoradiation (NCRT) for patients with rectal cancer. Materials and Methods We retrospectively reviewed the medical records of 524 rectal cancer patients who underwent NCRT and total mesorectal excision between January 2009 and December 2014. The performances of MRI with or without CEA parameters (initial CEA and CEA dynamics) for prediction of pathologic tumor response grade (pTRG) were compared by receiver-operating characteristic analysis with DeLong’s method. Cox regression was used to identify the independent factors associated to pTRG and disease-free survival (DFS) after NCRT. Results The median follow-up was 64.0 months (range, 3.0 to 113.0 months). On multivariate analysis, poor tumor regression grade on MRI (mrTRG; p < 0.001), initial CEA (p < 0.001) and the mesorectal fascia involvement on MRI before NCRT (mrMFI; p=0.054) showed association with poor pTRG. The mrTRG plus CEA parameters showed significantly improved performances in the prediction of pTRG than mrTRG alone. All of mrTRG, mrMFI, and initial CEA were also identified as independent factors associated with DFS. The initial CEA further discriminated DFS in the subgroups with good mrTRG or that without mrMFI. Conclusion The CEA parameters significantly improved the performance of MRI in the prediction of pTRG after NCRT for patients with rectal cancer. The DFS was further discriminated by initial CEA level in the groups with favorable MRI parameters.

Nonparametric multiplicative heteroscedasticity in multi-dimensional regression

유규상 한국통계학회 2017 Journal of the Korean Statistical Society Vol.46 No.3

In many statistical applications, the variability of the data is an important issue. For instance, in the regression analysis, researchers often meet the heteroscedasticity problem. There is a wide body of literature about the nonparametric estimation of the conditional variance function in one-dimensional case. However there are only few papers about the nonparametric estimation of the conditional variance function when there are several regressors in the model. In this paper, we propose a smooth backfitting estimator for the multiplicative conditional variance function and study the asymptotic property and finite sample performance via simulation studies.

On partial linear additive isotonic regression

유규상 한국통계학회 2014 Journal of the Korean Statistical Society Vol.43 No.1

In this paper we discuss semiparametric additive isotonic regression models. We discussthe efficiency bound of the model and the least squares estimator under this model. Weshow that the ordinary least square estimator studied by Huang (2002) and Cheng (2009)for the semiparametric isotonic regression achieves the efficiency bound for the regularestimator when the true parameter belongs to the interior of the parameter space. We alsoshow that the result by Cheng (2009) can be generalized to the case that the covariates aredependent on each other.

Risk Factors and Patterns of Locoregional Recurrence After Radical Nephrectomy for Locally Advanced Renal Cell Carcinoma

유규상,박원,표홍렬,정병창,전황균,강민용,서성일,전성수,이현무,최한용,박병관,김찬교,박성윤,권기영 대한암학회 2022 Cancer Research and Treatment Vol.54 No.1

Purpose We aimed to investigate the risk factors and patterns of locoregional recurrence (LRR) after radical nephrectomy (RN) in patients with locally advanced renal cell carcinoma (RCC). Materials and Methods We retrospectively analyzed 245 patients who underwent RN for non-metastatic pT3-4 RCC from January 2006 to January 2016. We analyzed the risk factors associated with poor locoregional control using Cox regression. Anatomical mapping was performed on reference computed tomography scans showing intact kidneys. Results The median follow-up duration was 56 months (range, 1 to 128 months). Tumor extension to renal vessels or the inferior vena cava (IVC) and Fuhrman’s nuclear grade IV were identified as independent risk factors of LRR. The 5-year actuarial LRR rates in groups with no risk factor, one risk factor, and two risk factors were 2.3%, 19.8%, and 30.8%, respectively (p < 0.001). The locations of LRR were distributed as follows: aortocaval area (n=2), paraaortic area (n=4), retrocaval area (n=5), and tumor bed (n=11). No LRR was observed above the celiac axis (CA) or under the inferior mesenteric artery (IMA). Conclusion Tumor extension to renal vessels or the IVC and Fuhrman’s nuclear grade IV were the independent risk factors associated with LRR after RN for pT3-4 RCC. The locations of LRR after RN for RCC were distributed in the tumor bed and regional lymphatic area from the bifurcation of the CA to that of the IMA.