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J Thorac Cardiovasc Surg 2003;126:551-557
© 2003 The American Association for Thoracic Surgery
General thoracic surgery |
a Department of Pathology and Laboratory Medicine, Cedars-Sinai Medical Center, Los Angeles, Calif, USA
b Department of Biostatistics, Cedars-Sinai Medical Center, Los Angeles, Calif, USA
c Department of Thoracic Surgery, Cedars-Sinai Medical Center, Los Angeles, Calif, USA
Received for publication July 15, 2002; revisions received August 19, 2002; revisions received October 2, 2002; accepted for publication October 18, 2002.
* Address for reprints: Alberto M. Marchevsky, MD, Cedars-Sinai Medical Center, 8700 Beverly Blvd, Los Angeles, CA 90048, USA
alberto.marchevsky{at}cshs.org
| Abstract |
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METHODS: Intrathoracic lymph nodes (n = 1063) from 60 patients with nonsmall cell carcinoma of the lung were studied for the presence of metastases with serial histologic sections and keratin immunostains. Metastases were classified as isolated tumor cells, pN1mi, pN1, pN2mi, and pN2. Isolated tumor cells were smaller than 0.2 mm, while pN1mi and pN2mi measured 0.2 mm to 2 mm. Survival analysis was performed, stratifying by nodal status and stage.
RESULTS: Isolated tumor cells were detected in 11 lymph nodes from 5 of 33 pN0 patients and in 9 pN1 and pN2 patients. The lymph nodes from 3 patients were reclassified as pN1mi. No pN2mi were detected. A survival model based on a stratification of the cohort into stages I to III was significant (chi-square = 7.426, df = 2, P = .024) but demonstrated considerable overlap between the survival curves of stage I and II patients. A model stratifying isolated tumor cells and pN1mi into stage I disease was significant (chi-square = 7.985, df = 2, P = .018) and showed no overlap between the survival curves of stage I and II patients. There were no significant survival function differences between patients with pN0, isolated tumor cells, and pN1mi.
CONCLUSIONS: Patients with nonsmall cell carcinoma of the lung with isolated tumor cells and pN1mi have similar survivals to those with pN0, consistent with the findings reported for breast cancer patients. Future larger studies of patients with nonsmall cell carcinoma of the lung are needed to confirm whether current American Joint Committee on Cancer staging criteria should be modified to include the pN1mi category.
Key Words: 10
The American Joint Committee on Cancer (AJCC) has recently published the sixth edition of the AJCC Cancer Staging Manual, including revised staging criteria for breast, colon, and other neoplasms.1 Staging criteria for lung cancer remain unchanged. The evaluation of the lymph node status of patients with nonsmall cell lung cancer (NSCLC) has been a source of controversy.2,3 Lymph node metastases can be subclassified into intranodal growth when the tumor is confined within the lymph node capsule and extranodal growth when there is neoplastic invasion of the soft tissues surrounding the nodal tissues. However, as demonstrated by Bollen and associates,4 it is seldom feasible to classify, on the basis of mediastinoscopy, a lymph node involvement as intranodal or extranodal, as portions of each lymph node rather than the entire intact lymph nodes are biopsied. This feature is not used for the routine staging of NSCLC patients or included in the current AJCC criteria for lung cancer.
Several studies have detected keratin-immunoreactive tumor cells in up to 63% of intrathoracic lymph nodes from NSCLC patients.5-10 The prognostic value of detecting these "occult metastases" or "micrometastases" in lung cancer and other neoplasms is the subject of intense research.5,11-18 Cote and associates3,19-22 indicated that "the accumulated evidence strongly suggests that the detection of occult regional and systemic metastases is an important predictor of disease progression." In a more recent study of 119 patients with T1, N0, and M0 adenocarcinoma and bronchioloalveolar carcinoma of the lung, Goldstein and associates12 reported "micrometastases" detectable by keratin immunohistochemistry in up to 8% of N0 patients. However, the overall sensitivity of the method was low, and positive cells were detected in only 0.5% to 1% of the lymph nodes examined. In one of their groups of patients who developed metastatic disease, the finding of micrometastases was significant for prognosis by multivariate analysis, but the authors concluded that due to the low sensitivity of the detection method, the use of immunohistochemical screening of lymph nodes for all N0 patients is questionable. Their study also confirmed the prognostic value of pathologic features such as vascular invasion, extensive central fibrosis, and high nuclear grade. Similar problems have been reported in studies of patients with esophageal, breast, and other neoplasms.5,11,14,23-27
The new AJCC Cancer Staging Manual proposes improved terminology for the classification of lymph node metastases. Isolated tumor cells (ITC) are defined as single tumor cells or small clusters of cells, smaller than 0.2 mm in greatest diameter.1 ITC can be seen on routine hematoxylin and eosin (H&E) stained sections (pNOi-, pNOmol-) or detected with the aid of immunohistochemistry (pNOi+) or molecular methods (pNOmol+). Micrometastases are clusters of tumor cells measuring between 0.2 mm and 2 mm in greatest diameter; they can usually be detected with routine histology and are classified as pN1mi or pN2mi according to their location. However, according to current AJCC criteria for lung cancer, NSCLC patients with a few intranodal tumor cells detected by routine histology or immunohistochemistry should be categorized as pN1 or pN2 according to their location. To our knowledge, it is unclear whether these patients have a similar prognosis as those with larger nodal metastases. We studied the prognostic value of detecting ITC in intrathoracic lymph nodes and distinguishing pN1mi and pN2mi from pN1 and pN2 in a group of 60 consecutive NSCLC patients who had long-term clinical follow-up.
| Methods |
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Estimation of nodal status
Based on the examination of the initial histologic slides, the initial nodal status of each patient was recorded. The lymph nodes were classified as pN0, pN1, and pN2 according to current AJCC criteria for NSCLC. The size of all lymph node metastases was measured with an eyepiece micrometer. The size of all metastases from the various lymph nodes from each patient was added to an aggregate tumor size per case and stratified into 3 categories: smaller than 0.2 mm, 0.2 mm to 2 mm, and larger than 2 mm. ITC detected in H&E-stained serial histologic sections were classified as pNOi-. They consisted of single or small groups of cells with cytologic features including a nuclear size larger than the diameter of 3 resting mature lymphocytes, anisocytosis, macronucleoli, irregular nuclear membranes, and/or high nucleo:cytoplasmic ratio. Cells with cytoplasmic keratin immunoreactivity that exhibited similar cytologic features, visible with the aid of the nuclear counterstain, were classified as pNOi+. The N status of each case was reclassified into 6 ordered categories, using the terminology proposed in the sixth edition of the AJCC cancer staging manual for breast cancer and other neoplasms: pN0, ITC (including pNOi- and pNOi+), pN1mi, pN1, pN2mi, and pN2. Figures 1 and 2 show examples of isolated tumor cells and micrometastases.
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| Results |
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The proportions of patients who survived their disease, by nodal status, are shown in Table 1. The survival proportions of pN0 cases (63.6%) did not change after ITC cases were removed from this group and reclassified as pN0i+ (64.3%). The survival proportions of pN1 patients declined considerably from 45.4% to 25% after cases with micrometastases were removed from this group and reclassified as pN1mi. All 3 patients with pN1mi survived. Figure 3 shows significantly different survival curves by initial nodal status (chi-square = 7.744, df = 2, P = .021). There were no significant differences in the survival functions of pN0 patients compared with those with ITC and pN1mi (chi-square = 0.001, df = 1, P = .975). Figure 4 shows no significant differences in the survival functions of patients with pN0i+ or pN1mi compared with those with pN1 (chi-square = 3.028, df = 1, P = .082). However, the graph shows 2 distinct survival curves and the lack of significant differences may result from the small sample size. Survival functions could not be compared across the pN1 and pN1mi categories due to the small number of patients. Figure 5 shows different survival curves for patients stratified by stages I to III (chi-square = 7.426, df = 2, P = .024). However, this model shows some overlap between the survival curves of stage I and II patients. Figure 6 shows different survival curves by stage when cases with ITC and pN1mi are classified as stage I disease (chi-square = 7.985, df = 2, P = .018). This model shows a distinct survival curve for stage I disease and some overlap between the survival curves of stage II and III disease.
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| Discussion |
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The study of lymph nodes with immunohistochemistry and the measurement of metastases did not contribute significant prognostic information to our pN2 patients. No instances of pN2mi were encountered in our 16 pN2 patients, and none of our 11 pN1 patients were upstaged as a result of these additional studies. These findings suggest that keratin immunohistochemistry is unlikely to be useful for the study of larger cohorts of pN1 and pN2 patients. Future studies with larger number of pN1 cases are needed to confirm the possible prognostic value of identifying pN1mi.
Our study raises questions regarding the practical role of immunohistochemistry for the study of lymph node metastases in patients with NSCLC. Several previous studies have reported that the finding of keratin immunoreactive tumor cells in approximately 4% to 63% of lymph nodes from NSCLC patients is usually associated with a less favorable prognosis.5-8,10,28,29 However, various definitions for "micrometastases" or "occult metastases" have been used; the size of the metastases has not always been reported and relatively small numbers of patients have been studied.30-32 Potential sources of variability include the study of only N0 patients by some investigators and of N0 to N3 by others and the use of different antibodies and/or immunohistochemical detection methods.12 Our data support the suggestion by Goldstein and associates12 that although ITC can be detected with immunohistochemistry in a significant number of previously negative lymph nodes, many of them are seen in NSCLC patients with other positive pN1 and pN2 lymph nodes. Slightly less than half of the lymph nodes with immunoreactive ITC encountered in our study were detected in the negative lymph nodes from patients with other positive pN1 and pN2 lymph nodes; the stage of these patients remained unchanged.
The influence of the size of intranodal metastases on the prognosis of NSCLC patients has not been studied extensively, to our knowledge. Bollen and associates4 demonstrated that NSCLC patients with "minimal disease," characterized by the presence of a single, small metastatic focus, had significantly better survival rates than N2 patients with more extensive nodal involvement.
Molecular methods may offer a more sensitive and cost-effective method for the detection of occult micrometastases in the future, but it is unclear if these findings are going to provide prognostic information for NSCLC patients. Salerno and associates18 demonstrated the presence of MUC1 RNA in histologically negative lymph nodes from NSCLC patients, using reverse-transcriptase-polymerase chain reaction. Recently DAmico and colleagues33,34 and Ahrendt and coworkers35 have applied molecular methods to the assessment of lymph nodes in patients with resected stage I NSCLC. Occult lymph node metastases identified based on the presence of p53 and k-Ras mutations are found in up to 50% of patients but do not correlate with overall survival.35 DAmico and colleagues33,34 have demonstrated that expression levels of markers such as p53, urokinase plasminogen activator, E-cadherin, and ErbB2 correlated with the rate of brain metastases.
It is premature to speculate how stage I and II NSCLC patients will be managed in the future based on the detection of micrometastatic disease, as current postoperative therapeutic modalities are not very effective. To our knowledge, breast cancer patients with micrometastases are currently not being treated with chemotherapy, although this option is offered to pN1 patients.19
In conclusion, NSCLC patients with ITC and pN1mi have similar survival rates as those with pN0, results that are consistent with those already reported for breast cancer and other cancer patients. Lymph nodes with ITC should probably not be classified as pN1 until future studies demonstrate a clear prognostic value for this finding. Larger groups of NSCLC patients with stage II disease need to be studied for the distinction of pN1mi versus pN1 to determine whether current AJCC staging criteria for NSCLC patients need to be modified.
| Acknowledgments |
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