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Ann Thorac Surg 2007;84:973-980
© 2007 The Society of Thoracic Surgeons
a Department of Thoracic and Cardiovascular Surgery, The University of Texas MD Anderson Cancer Center, Houston, Texas
b Department of Pathology, The University of Texas MD Anderson Cancer Center, Houston, Texas
Accepted for publication March 26, 2007.
* Address correspondence to Dr Rice, Department of Thoracic and Cardiovascular Surgery, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Unit 445, Houston, TX 77030 (Email: drice{at}mdanderson.org).
| Abstract |
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Methods: We retrospectively evaluated all patients who underwent pulmonary resection for NSCLC during a 20-year period at the University of Texas MD Anderson Cancer Center and compared recurrence and survival rates of patients with SARC with a cohort of patients with typical NSCLC. To account for known prognostic factors such as smoking status, age, gender, pathologic stage, and adjuvant therapy, we used one-to-one matching based on propensity scores.
Results: The study included 63 SARC patients and 1133 NSCLC patients with complete data. Propensity score matching identified 63 NSCLC patients that were similar to the 63 SARC patients from known clinical factors. The 5-year survival for SARC patients was 24.5% compared with 46.3% for NSCLC patients (p = 0.01); median time to recurrence was 11.3 months and 61.4 months, respectively (p = 0.001).
Conclusions: Compared with other histologic subtypes, SARC behaves in an aggressive fashion. These tumors are frequently symptomatic, are locally advanced, and have higher rates of recurrence. Future investigation of novel treatment approaches is warranted. Nonsurgical treatment modalities may be appropriate for patients with clinically advanced disease.
| Introduction |
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Sarcomatoid histology is rare and found only in 0.1% to 0.4% of all patients with non-small cell lung cancer (NSCLC) [1]. Its prognostic significance is controversial, with some reports suggesting a poor prognosis [2–10] and others showing no difference between SARC and typical NSCLC [11, 12]. However, most publications on SARC have been small case series focusing on pathologic descriptions [2–5, 8–11, 13–19], with little information about clinical outcomes. The existing literature lacks a stage-adjusted, concurrent comparison of a large series of SARC patients with typical NSCLC patients treated at the same institution. Therefore, the goal of this study was to assess the prognostic significance of SARC versus typical NSCLC by comparing propensity score–matched patients from a single institution for recurrence and survival outcomes.
| Patients and Methods |
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Patients
An institutional database was used to identify 3574 patients who underwent any form of pulmonary surgical procedure for primary lung cancer at UTMDACC from the beginning of 1984 through June 2003. The study included 1133 patients with complete clinical data available who underwent resection of typical NSCLC and 63 who were identified with a pathologic diagnosis of SARC. NSCLC patients with carcinoid histology as the criterion for primary lung cancer were excluded owing to a better-than-usual prognosis for this subgroup [20] that could overestimate the differences in survival seen when SARC and NSCLC patients were compared.
Most patients were staged preoperatively with chest roentgenogram and computed tomography scan of the chest. Additional staging studies such as mediastinoscopy, brain and bone imaging, and positron emission tomography were performed at the discretion of the surgeon or oncologist. Complete anatomic lung resections were done whenever possible and appropriate. Mediastinal and hilar lymph nodes were sampled or completely dissected, depending on surgeon preference. Pathologic stage was assigned according to the New International Staging System for Lung Cancer [21], irrespective of the staging system in use at the time of surgery.
Patients were followed up with a chest roentgenogram and a clinical visit 1 month postoperatively, then at 6-month intervals for 2 years, and annually thereafter, unless new symptoms prompted more intensive evaluation. Vital status was determined from the medical record and the Social Security Death Index. Demographics, smoking history, comorbidities, clinical and pathologic stage, treatment strategies, operative data, follow-up duration, and survival and recurrence data were collected on all patients.
Pathology
Surgical pathology slides of patients with SARC were reviewed by lung pathologists at UTMDACC to ensure accuracy of histologic diagnosis. In all cases, hematoxylin-and-eosin stained histologic slides and, when available, immunohistochemical preparations were used to confirm the epithelial differentiation (eg, keratin positivity) of the tumor. The diagnosis of SARC was confirmed when at least 10% of the tumor contained a sarcomatoid component consisting of spindle or pleomorphic giant cells, or both.
Data Analysis
Associations between categoric variables were assessed by Pearson
2 or Fisher exact tests. Continuous data were compared using the Student t test and expressed as mean ± standard deviation. Factors associated with SARC histology were identified using multiple logistic regression with Wald stepwise backwards elimination, followed by a test for forward selection.
Because other studies have suggested that SARC occurs more often in heavy smokers and tends to present at a more advanced stage, both of which would confound survival results, we chose to match SARC and NSCLC patients in a one-to-one fashion by using all available clinical data. This was performed by constructing propensity scores [22–24] using all preoperative variables that might influence recurrence and survival, including age, gender, year of operation, pathologic tumor stage (T), nodal stage (N), and metastatic stage (M), preoperative chemotherapy, preoperative radiation, smoking history, timing of smoking cessation, prior cancer, and prior treatment with chemotherapy or radiation. Pair-wise matches were based on the nearest propensity scores. Because of clustering of scores, higher order matching was not done. The propensity-matched NSCLC and SARC subjects (63 in each group) were compared using the McNemar nonparametric test for two-by-two categoric data [25], the marginal homogeneity test for multinomial data [26, 27], and two-sample t test for continuous data.
Survival time was calculated from date of treatment initiation to date of death to avoid biasing survival times against patients receiving preoperative treatment. All-cause mortality was used as the survival end point. Recurrence was calculated from date of treatment initiation to the date of the first documented recurrence. Recurrence and survival curves were calculated using the Kaplan-Meier method [28], and group comparisons were made by using the log-rank test. A value of p
0.05 was considered statistically significant. All data entry and analyses were performed using SPSS 13.0 software (SPSS Inc, Chicago, IL).
| Results |
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| Comment |
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Another study that investigated comparative survival for SARC and NSCLC within the same institution was by Nakajima and colleagues [11], who described 37 patients with SARC and compared outcomes with 647 patients who underwent surgical resection for typical NSCLC. No significant differences in survival were found between groups, which is surprising considering 57% of SARC patients were p stage III. Specific survival rates were not described, however, and they did not perform multivariable analysis or stage-matched comparisons.
A study by Pelosi and colleagues [12] examined outcomes of 31 patients with SARC from two separate time periods and from two separate institutions and compared survival of SARC patients with typical survival rates for NSCLC patients, but there was no control group of patients treated under the same circumstances as the SARC patients. Unlike the series we report, only 13% of SARC patients were stage III, and comparisons of survival were limited to patients with early stage disease (p stage I) and were based on cancer-related deaths only. The authors did not identify any significant survival differences, and specific survival rates were not described. Nonetheless, the fact that survival in early stage patients was similar to that of patients with typical NSCLC is interesting.
It has been postulated that the aggressive nature of SARC is at least in part attributable to the sarcomatoid elements, which are believed to develop enhanced angiogenic activity as well as tumor cell motility [12]. The proportion of sarcomatoid elements frequently correlates with tumor size, and it is therefore possible that smaller, earlier-stage tumors may not contain sufficient sarcomatous elements to negatively impact survival rates compared with typical NSCLC.
Unfortunately, these reports are limited in their ability to truly define the prognostic significance of sarcomatoid histology because of confounding variables that prevent accurate survival comparisons to be made between SARC and typical NSCLC groups. We attempted to compensate for known prognostic variables such as pathologic stage, treatment received, age, gender and other factors possibly influencing survival; therefore, the contribution of SARC histology to the biologic tumor behavior can be more accurately determined. We found significantly worse survival and higher recurrence rates associated with SARC histology.
The median survival of patients with SARC was 17.4 months, which is slightly longer than that reported in other published series, even though 43% of patients were stage III or higher. It is possible that this is related to an inherently better prognosis for patients who were fit enough to undergo surgery, but an aggressive multimodality therapeutic approach may have also contributed. Patients in many other series reported in the literature have either been identified from autopsy results or were not uniformly treated with curative intent. However, despite a policy of aggressive treatment for patients with SARC, survival was significantly less than that of stage-matched controls and was particularly poor for patients with SARC of advanced clinical stage. There were no 5-year survivors among patients with tumors of p stage III or greater.
Compared with patients with typical NSCLC, both local and distant recurrence rates were high in SARC patients. Although the benefit of postoperative radiation therapy has not been shown to improve survival for patients with typical NSCLC, that 27% of recurrences occurred locally in the chest wall argues strongly for its use in cases where tumors invade the parietal pleura or chest wall.
There are little published data on the use of adjuvant chemotherapy in patients with SARC. Raveglia and colleagues [7] described 14 patients with p stage II or III SARC who underwent resection, followed by cisplatin-based chemotherapy. Median survival was 7 months versus 26 months for 6 patients with stage I disease who did not receive adjuvant therapy. Because the efficacy of adjuvant chemotherapy has been documented for patients with NSCLC stage IB or higher [30–32], and 87% of patients in our series who recurred did so at distant sites (52% overall), it seems prudent to consider the use of adjuvant chemotherapy after resection. Preoperative chemotherapy or radiation therapy was administered to 28% and 30% of matched SARC and NSCLC patients, respectively. Because of the small sample size, their contribution to outcome is uncertain, however. In addition, the ability to apply a preoperative regimen depends upon the diagnosis of SARC histology being made before the surgical procedure. In practice, this is frequently not possible, either because not all lung masses are routinely biopsied preoperatively or because of tumor sampling error.
This study has several limitations that must be considered when interpreting the results. Being a retrospective study, it is subject to inherent biases of patient selection, therapeutic decision-making, and variations in quality of recorded data. It is certainly possible that a greater proportion of patients with advanced SARC were referred to our tertiary referral center for care; however, by performing propensity scoring, we attempted to compensate for this potential imbalance. This study included only patients who underwent a surgical procedure, therefore excluding what are likely to be more advanced stage patients. There may be a disparity in nonsurgical patient distribution in the two groups, and our study design does not allow us to determine this distribution.
A retrospective, histologic review of pathology from the control NSCLC patients was not performed. It is therefore possible that some patients with SARC histology were misclassified in the NSCLC group. However, if this were the case, we would expect a reduction in the observed differences in survival and recurrence between groups.
Finally, because of the rarity of SARC, our sample size is small, thus limiting generalizability. Nevertheless, it would be difficult to obtain a larger sample size of SARC patients unless data from multiple institutions were pooled.
In summary, in patients undergoing surgical resection for NSCLC, the SARC histologic variant is associated with significantly worse prognosis, both for long-term survival and for early recurrence of disease. Use of adjuvant chemotherapy and radiation should be considered for patients with bulky tumors, chest wall invasion, or nodal involvement because of the high incidence of both local and distant failure after resection. For patients with stage III or IV SARC tumors identified preoperatively, nonoperative treatment may be appropriate given the poor outcomes with surgical resection in advanced stage patients.
| Acknowledgments |
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