RESUMEN
Since the seminal introduction of the propensity score by Rosenbaum and Rubin, propensity-score-based (PS-based) methods have been widely used for drawing causal inferences in the behavioral and social sciences. However, the propensity score approach depends on the ignorability assumption: there are no unobserved confounders once observed covariates are taken into account. For situations where this assumption may be violated, Heckman and his associates have recently developed a novel approach based on marginal treatment effects (MTE). In this paper, we (1) explicate consequences for PS-based methods when aspects of the ignorability assumption are violated; (2) compare PS-based methods and MTE-based methods by making a close examination of their identification assumptions and estimation performances; (3) apply these two approaches in estimating the economic return to college using data from NLSY 1979 and discuss their discrepancies in results. When there is a sorting gain but no systematic baseline difference between treated and untreated units given observed covariates, PS-based methods can identify the treatment effect of the treated (TT). The MTE approach performs best when there is a valid and strong instrumental variable (IV). In addition, this paper introduces the "smoothing-difference PS-based method," which enables us to uncover heterogeneity across people of different propensity scores in both counterfactual outcomes and treatment effects.
RESUMEN
The present study reports the case of a 39-year old male patient with a recurrent waist tumor that occurred subsequent to percutaneous nephrolithotomy (PCNL). The patient initially underwent PCNL for the management of right calculus of the kidney. Six years later, the patient underwent local mass resection for a tumor at the waist, which was subsequently diagnosed as adenocarcinoma. However, seven months subsequent to local resection, the patient presented to the Affiliated Cancer Hospital of Xiangya Medical School with a one-month history of a recurrent tumor located at the right waist. Physical examination identified no visible skin lesions; however, a palpable hard nodule was present over the right waist. Imaging studies, consisting of computed tomography (CT) and positron emission tomography-CT, indicated no additional metastases. Therefore, the patient underwent local mass resection of the waist tumor. Subsequent histological examination determined a diagnosis of metastatic adenocarcinoma. Considering the previously conducted PCNL surgery and the diagnosis, it is proposed that the recurrent waist tumor originated from renal cell carcinoma (RCC), also termed renal adenocarcinoma. However, no evidence of the original RCC tumor was identified. Therefore, the selection of an effective treatment strategy was challenging.
RESUMEN
In the present study, the case of a 51-year-old female with a metastatic tumor in the left kidney originating from cervical carcinoma, is reported. The patient had undergone chemoradiotherapy for stage IIB squamous-cell carcinoma of the uterine cervix 3 years earlier. Computed tomography (CT) identified low-density left renal nodules, which were diagnosed post-operatively as renal cysts during the follow-up conducted 2 years later. The next year, the patient was admitted to the Hunan Provincial Tumor Hospital (The Affiliated Tumor Hospital of Xiangya Medical College, Central South University, Changsha, Hunan, China) with a fever of unknown origin, left-sided flank pain and hematuria. CT examination detected irregular low-density nodules in the left kidney and heterogeneous enhancement on enhanced CT. Subsequently, the patient was subjected to a nephrectomy. Post-surgical analysis of subsequent biopsies indicated kidney tumor metastasis originating from cervical carcinoma. Renal metastases are rare in patients with cervical carcinoma. The present study reported a case of renal metastasis originating from cervical carcinoma and also reviewed previous case reports on patients presenting with this unusual type of cancer.