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Ann Thorac Surg 2005;79:278-282
© 2005 The Society of Thoracic Surgeons

Original article: General thoracic

Histopathologic Prognostic Factors in Resected Colorectal Lung Metastases

Satoshi Shiono, MDa,b, Genichiro Ishii, MDa, Kanji Nagai, MDb, Junji Yoshida, MDb, Mitsuyo Nishimura, MDb, Yukinori Murata, MTc, Koji Tsuta, MDa, Yutaka Nishiwaki, MDb, Tetsuro Kodama, MDd, Atsushi Ochiai, MDa,*

a Pathology Division, National Cancer Center Research Institute East, National Cancer Center Hospital East, Chiba, Japan
b Division of Thoracic Oncology, National Cancer Center Hospital East, Chiba, Japan
c Clinical Laboratory Division, National Cancer Center Hospital East, Chiba, Japan
d Department of Respiratory Oncology, National Cancer Center Hospital, Tokyo, Japan

Accepted for publication June 21, 2004.

* Address reprint requests to Dr Ochiai, Pathology Division, National Cancer Center Hospital East, 6-5-1 Kashiwanoha, Kashiwa, Chiba 277-8577, Japan (E-mail: aochiai{at}east.ncc.go.jp).


   Abstract
Top
 Abstract
Introduction
 Patients and Methods
 Results
 Comment
 References
 
BACKGROUND: Pulmonary metastasectomy is a standard method of treatment for selective pulmonary metastases of colorectal cancer. However, the pathologic factors of metastatic lesions that affect survival and tumor recurrence after pulmonary resection are less well defined. The pathologic findings of colorectal pulmonary metastases have not been correlated with clinical outcome. The study was conducted to clarify the characteristics and identify the prognostic factors of the pulmonary metastases of colorectal cancer.

METHODS: Between July 1992 and November 2002, 89 patients underwent the complete resection of pulmonary metastases of primary colorectal carcinoma, and we pathologically reviewed the surgical specimens of 136 metastatic lesions from these patients.

RESULTS: There were no perioperative deaths. The overall 5-year survival rate was 61.4%. No clinical factors were associated with the outcome. The univariate analysis of pathologic factors revealed aerogenous spread with floating cancer cell clusters (ASFC) (p = 0.004), vascular invasion (p = 0.002), lymphatic invasion (p = 0.032), and pleural invasion (p = 0.037) to be prognostic factors. The multivariate analysis showed vascular invasion (p = 0.02) and ASFC (p = 0.02) to be independent prognostic factors. The 5-year survival rate of patients whose lesions were positive for both ASFC and vascular invasion was 24.7% and much poorer than in the patients with ASFC without vascular invasion (78.6%), vascular invasion but without ASFC (80.2%), and patients negative for both (93.3%) (p = 0.0002).

CONCLUSIONS: The morphologic features of ASFC and vascular invasion at metastatic sites are prognostic factors for colorectal cancer patients who have undergone pulmonary metastasectomy.


   Introduction
Top
 Abstract
 Introduction
Patients and Methods
 Results
 Comment
 References
 
Longer survival after surgery for pulmonary metastases of colorectal carcinoma has been documented [1–18], with 5-year survival ranging from 32.4% to 63.7%. Because no form of chemotherapy has been found to significantly improve the survival of colorectal cancer patients with pulmonary metastases, surgery is an effective treatment.

Many articles have described the benefits of surgery for pulmonary metastases of colorectal carcinoma [1–18], but the pathologic factors of metastatic lesions that affect survival and tumor recurrence after pulmonary resection are less well defined. To clarify the characteristics and identify the prognostic factors of the pulmonary metastases of colorectal cancer, we pathologically reviewed surgically resected specimens and identified prognostic factors for patients who have undergone pulmonary metastasectomy.


   Patients and Methods
Top
 Abstract
 Introduction
 Patients and Methods
Results
 Comment
 References
 
Between July 1992 and November 2002, 88 patients underwent resection of pulmonary metastases of primary colorectal carcinoma at the Division of Thoracic Oncology of the National Cancer Center Hospital East, Chiba, Japan, and were retrospectively reviewed from medical records. Before thoracotomy, we performed whole body computed tomography (CT) and endoscope. The primary colorectal cancer was controlled, and all of the patients tolerated pulmonary resection well. Serum carcinoembryonic antigen (CEA) level was measured before thoracotomy.

After excluding 1 patient because the pathologic specimen was damaged during the surgical procedure, 87 patients (57 men and 30 women) were eligible for this study. The median age of the patients at the time of pulmonary metastasectomy was 61 years (range: 23 to 82). The primary site was the colon in 47 patients and the rectum in 37 patients. In 3 patients it was unknown whether the primary site was the colon or the rectum, because the colorectal resections had been performed at other hospitals.

As a rule, we perform limited resection for metastatic nodules, but we select lobectomy or pneumonectomy if the tumor is located in the hilum, if multiple nodules are present in the same lobe, or if the tumor is larger than 3.0 cm. When metastatic lesions are located in the peripheral third of the lung and are 3.0 cm or less in size, thoracoscopic surgery is indicated. The surgical procedure was lobectomy in 25 patients, segmentectomy in 17 patients, wedge resection in 43 patients, bilobectomy in 1 patient, and pneumonectomy in 1 patient. Twenty-two patients underwent a second pulmonary metastasectomy, and 1 patient underwent a third.

A total of 136 pulmonary metastatic lesions were resected, and from 1 to 5 metastatic lesions were resected per patient. At the time of the first thoracotomy, 66 patients had 1 metastasis, 9 had 2, 8 had 3, 3 had 4, and 1 patient had 5.

Before the pulmonary metastases were resected, 28 patients underwent surgery for extrapulmonary metastatic lesions. Twenty-three had undergone hepatectomy, and 1 patient each had undergone hepatectomy and adrenalectomy, hepatectomy and abdominal lymph node dissection, resection of local recurrence in the colon, resection of a skin metastasis, and inguinal lymphadenectomy. Eleven patients had received systemic chemotherapy before the pulmonary metastases were resected, and 2 patients received chemotherapy after pulmonary metastasectomy. The median follow-up period after the first pulmonary resection was 32 months (range: 1 to 110 months).

Histologic Analysis
The examinations were performed by two pathologists (S.S. and G.I.) who were blinded to the clinical information. The surgically resected specimens were fixed in 10% formalin or methanol and cut into slices of 5 to 10 mm. All sections that contained both tumor tissues and surrounding normal lung tissue were embedded in paraffin. Additional consecutive 5 µm sections were cut from a selected tissue block and stained with hematoxylin and eosin (HE), Alcian blue–periodic acid-Schiff (AB-PAS), and Victoria van Gieson stain.

We examined the section that contained the largest diameter of tumor for degree of tumor differentiation, micrometastases, bronchial invasion, aerogenous spread with floating cancer cell clusters (ASFC) around the main tumor, vascular invasion, lymphatic invasion, bronchial invasion, pleural invasion, surgical margin, and lymph node metastasis in the patients in which lymph node dissection was performed. The criterion for ASFC was the presence of tumor clusters lying free in the alveolar space and at least 0.5 mm from the main metastatic lesion (Fig 1).



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  		Fig 1. (A) The criterion for aerogenous spread with floating cancer cell clusters was the presence of tumor clusters floating in the alveolar space (black square) and separated from the main metastatic lesion by at least 0.5 mm (black line) (original magnification, x50). (B) An enlargement of the tumor clusters within the black square in (A) (original magnification, x120).

 
We defined a micrometastasis as a tumor detected histologically and not by preoperative chest CT. We also used Victoria van Gieson staining to evaluate the sections for vascular invasion. When more than one pulmonary metastasis was evident, the most advanced features were recorded as representative.

Statistical Analysis
Overall survival was analyzed by the Kaplan-Meier method, and differences in variables were calculated by the log-rank test. Cox's proportional hazards model was used for multivariate analysis. The data were calculated by using version 5.0 of the StatView software package (SAS Institute Inc, Cary, NC). A p value of less than 0.05 was considered indicative of statistical significance.


   Results
Top
 Abstract
 Introduction
 Patients and Methods
 Results
Comment
 References
 
No perioperative deaths occurred. The median interval between colorectal resection and the diagnosis of the pulmonary metastasis (disease-free interval [DFI]) was 24.3 months. The overall 5-year survival from the first lung resection was 61.4% (Fig 2). We assessed clinical factors, including gender, age, DFI, primary site, whether hepatectomy had been performed, tumor size, solitary or multiple tumors, serum CEA level, and surgical procedure as prognostic factors but did not identify any clinical factors significantly related to survival.



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  		Fig 2. Overall survival of the 87 patients after pulmonary metastasectomy. The 5-year survival was 61.4%.

 
Histopathologic Findings
Table 1 summarizes the histopathologic findings and survival. The metastases ranged in size from 0.7 cm to 6.7 cm, and their median size was 1.8 cm. The metastases were well-differentiated adenocarcinoma in 15 patients, moderately differentiated adenocarcinoma in 71 patients, and 1 lesion was poorly differentiated adenocarcinoma. Micrometastases were found in 25 patients (29%). ASFC around the main lesion was observed in 36 patients (41%). The distance of the ASFC from the main tumor ranged from 0.5 mm to 11.0 mm (median: 2.0 mm). Ten of the 45 patients with bronchial invasion showed endobronchial growth. Vascular invasions were observed in 48 lesions (55%). Lymphatic invasion in bronchovascular bundles was detected in 36 patients (41%). Fourteen patients had pleural invasion (16%), with pleural invasion extending to the visceral pleura in 11 patients and involving the parietal pleura in the other 3 patients. Tumor cells were detected at the surgical margin in 5 patients. Six of the 9 patients in whom lymph nodes were dissected or biopsies were performed were positive for lymph node metastasis.


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  		Table 1. Survival of 87 Patients According to Pathologic Findings of Pulmonary Metastases
 
Survival
Figure 3A shows the survival curves in the patients with and without ASFC. The 5-year survival rate of the patients with ASFC was 46.9% versus 88.2% in the patients without ASFC (p = 0.004).



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  		Fig 3. Survival curves of the patients after pulmonary metastasectomy (A) with and without aerogenous spread with floating cancer cells (ASFC), (B) with and without vascular invasion, (C) with and without lymphatic invasion, and (D) with and without pleural invasion.

 
The 5-year survival rate in the patients who were positive for vascular invasion was 39.9% and significantly worse (p = 0.002) than the 85.8% in the negative patients (Fig 3B).

The 5-year survival rate of the patients with lymphatic invasion was 47.0% and significantly worse than that of the patients without lymphatic invasion (78.4%) (p = 0.032) (Fig 3C).

The survival of the patients who were positive for pleural invasion (49.5%) was also significantly worse than in the negative patients (63.5%) (p = 0.037) (Fig 3D).

Cox's proportional hazards mode was used to perform multivariate analysis with the variables of vascular invasion, lymphatic invasion, pleural invasion, and ASFC. Both vascular invasion and ASFC factors were shown to be independent prognostic factors (p = 0.02) (Table 2), and we divided the patients into four groups according to whether these factors were present or not. The 5-year survival rate of the patients with both ASFC and vascular invasion was 24.7% and much poorer than that of the patients with ASFC and without vascular invasion (78.6%), the patients with vascular invasion without ASFC (80.2%), and the patients negative for both (p = 0.0002) (Fig 4).


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  		Table 2. Relationship of Individual Variables to Outcome (Cox's Proportional Hazards Model)
 


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  		Fig 4. Survival curves of patients after pulmonary metastasectomy based on four groups obtained by dividing by the patients according to the presence or absence of aerogenous spread with floating cancer cell clusters (ASFC) and vascular invasion (v).

 

   Comment
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
References
 
The results of this study revealed a 5-year survival after pulmonary metastasectomy of 61.4%, which was better than in other reports. The explanation may be because the patients were strictly selected by a multimodal assessment in our institute to achieve complete curative resection. An alternative explanation is that, as Goya and colleagues indicated, the 5-year survival after thoracotomy may reflect a length bias caused by the biologic behavior of the metastatic pulmonary lesions [12].

Several factors, including DFI [6, 10, 11], the number of pulmonary metastases [1, 2, 5–7, 10, 13–16, 18], and serum CEA level before pulmonary metastasectomy [2–5, 7, 9, 11, 13, 14] have been reported to be correlated with outcome. Irshad and colleagues reported that the patients in whom the pathologic findings of the primary colorectal cancer were moderately or poorly differentiated cancer had a poor survival [10], while Ike and associates also found that patients with well-differentiated adenocarcinoma in the primary tumor were likely to be long-term survivors [6].

Ishikawa and colleagues reported that another morphologic factor, the presence of extranodal cancer deposits in the primary colorectal cancer, was a significant indicator of a poor outcome after surgery for colorectal lung metastases [18]. The maximum diameter of the metastases [13, 15] and the presence of hilar or mediastinal lymph node involvement have also been related to a poor outcome [1–4].

By contrast, Zanella and colleagues reported that differences in the site and stage of primary colorectal cancer, the number of pulmonary metastases, and DFI between the time of initial treatment of the primary tumor and the diagnosis of lung metastases appeared to have no influence on overall survival or DFI after metastasectomy [8]. Because the patients' backgrounds in our study were different from other reports owing to our strict selection, we were unable to identify any prognostic clinical factors in the present study.

Most of these previously discussed studies focused on morphologic examination of primary tumors, and there had been only one report on the histologic appearance of metastatic lesions. Shirakusa and colleagues reported that the lesions of the patients who underwent pulmonary metastasectomy could be divided into two types—an infiltrative type and a noninfiltrative type—according to the histologic appearance of the tumor margin of the metastatic lesion [19]. They defined the infiltrative type as a metastatic tumor that had invaded the surrounding lung parenchyma, the same as observed in the primary lung cancer lesion. The 5-year survival was worse in the infiltrative-type patients, and the lymph node metastasis rate was higher. Because the number of patients in their study was quite small and the morphologic definition of cancer infiltration into surrounding lung parenchyma was unclear, no correlations between the pathologic features and pattern of recurrence has been demonstrated.

In the current study, 5 patients showed malignant-positive surgical margin. In these 5 patients, ASFC was noted in 3 patients and vascular invasion in 2 patients. However, as shown in Table 1, we could not find the relationship between surgical margin and prognostic factors.

The results of this study showed that ASFC, vascular, lymphatic, and pleural invasions were associated with poor outcome of patients with pulmonary metastasis of colorectal cancer. Multivariate analysis revealed two morphologic factors, ASFC and vascular invasion, as independent prognostic factors. When these two factors were combined, the patients with ASFC and vascular invasion were found to have a worse outcome, while the patients negative for both had a better outcome. These factors may reflect the biologic aggressiveness of malignant cancer cells. Although the molecular mechanisms of ASFC and vascular invasion by pulmonary metastases of colorectal cancer are still unclear, the loss of cell-to-cell adhesion or anchorage-independent growth of cancer cells may contribute to ASFC and vascular invasion. Clarifying the mechanisms of ASFC and vascular invasion would provide insight into the aggressive behavior of metastatic colon cancer. We are now attempting to identify molecular markers for ASFC and vascular invasion.

In this study we identified effective pathologic prognostic markers for colorectal cancer patients who have undergone pulmonary metastasectomy. Although no adjuvant therapy has been available after pulmonary resection, clinical trials may be needed for patients with ASFC and vascular invasion.


   References
Top
 Abstract
 Introduction
 Patients and Methods
 Results
 Comment
 References
 

  1. Okumura S, Kondo H, Tsuboi M, et al. Pulmonary resection for metastatic colorectal cancer: experiences with 159 patients J Thorac Cardiovasc Surg 1996;112:867-874.[Abstract/Free Full Text]
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  3. Saito Y, Omiya H, Kohno K, et al. Pulmonary metastasectomy for 165 patients with colorectal carcinoma: a prognostic assessment J Thorac Cardiovasc Surg 2002;124:1007-1013.[Abstract/Free Full Text]
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  6. Ike H, Shimada H, Ohki S, Togo S, Yamaguchi S, Ichikawa Y. Results of aggressive resection of lung metastases from colorectal carcinoma detected by intensive follow-up Dis Colon Rectum 2002;45468–77.
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  8. Zanella A, Marchet A, Mainente P, Nitti D, Lise M. Resection of pulmonary metastases from colorectal carcinoma Eur J Surg Oncol 1997;23424–32.
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