The sentinel node procedure in colon carcinoma: a multi-centre study in The Netherlands
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Lymph node status is the most important predictive factor in colorectal carcinoma. Recurrences occur in 20% of the patients without lymph node metastases. The sentinel lymph node (SLN) biopsy is a tool to facilitate identification of micrometastatic disease and aberrant lymphatic drainage. We studied the feasibility of in vivo SLN detection in a multi-centre setting and evaluated nodal micro-staging using immunohistochemistry (IHC).
Materials and methods
Sub-serosal injection with Patent Blue dye was used in the SLN procedure in 69 patients operated for localized colon cancer in six Dutch hospitals. Each SLN was examined with routine haematoxylin–eosin staining. In tumour-negative SLNs, we performed CK7/8 or 18 IHC.
The procedure was successful in 67 of 69 patients (97%). The SLN was negative in 43 patients. In three cases, it was false negative, resulting in a negative predictive value of 93% and an accuracy of 96%. In 24 of 27 patients with lymph node metastases in a successful SLN procedure, the SLN was positive (sensitivity 89%). In 15 patients, the SLN was the only positive node (21%). In nine patients, we only found micrometastases or isolated tumour cells, resulting in 18% upstaging. Aberrant lymphatic drainage was seen in three patients (4%).
The SLN procedure in localized colon carcinoma is reliable in a multi-centre setting. It is helpful to identify patients who would be classified as stage II with conventional staging (18%) and who might benefit from adjuvant treatment.
KeywordsColon carcinoma Sentinel lymph node Micrometastasis Minimal residual disease
Survival in patients with colon carcinoma is strongly correlated with lymph node status: the 5-year disease-free survival rate is 70–80% for patients with lymph node-negative disease (stage I/II) but only 45–50% for those with node-positive disease (stage III) . The presence of lymph node metastases indicates the use of adjuvant chemotherapy in these patients, which increases the 5-year survival rate with about 10% . Despite the favourable prognosis of patients with localized colon carcinoma without regional lymph node metastasis, 20–30% of these patients will develop recurrent disease after apparently curative resection . It is possible that in this group of patients, small lymph node metastases have been missed, resulting in understaging. This may be due to an inadequate surgical lymphadenectomy or insufficient pathological examination . According to international guidelines, meticulous pathological examination of at least 12 lymph nodes is warranted for adequate staging of patients with colon carcinoma . However, several studies showed that the minimal number of lymph nodes necessary for correct staging varied considerably from 6 to 18 to as many as possible in the study of Goldstein et al. [4, 6, 7, 8, 9]. In addition, in-depth pathological examination of lymph nodes by immunohistochemical staining for cytokeratin or reverse transcriptase polymerase chain reaction (RT-PCR) may reveal micrometastases that could have been missed by routine haematoxylin and eosin (H&E) examination. Several authors have reported a decreased survival rate when micrometastases are detected in colon carcinoma [10, 11, 12, 13]. The possible benefit of adjuvant therapy in this group of patients is not clear yet.
These (ultra-)staging techniques are time consuming, labour intensive and costly. For optimal staging, in depth examination of only the sentinel lymph node (SLN) could be helpful. In colon carcinoma, the SLNs are defined as the first one to four blue-stained nodes with the most direct lymph drainage from the primary tumour. They have the greatest potential to harbour metastatic disease when present, enabling focussed examination with multi-level micro-sectioning of the SLNs to provide a more efficient and cost-effective detection of micrometastases. In addition, patterns of aberrant lymphatic drainage can be visualized with SLN mapping, which may lead to a more extended resection. Several studies have reported varying results of the SLN procedure in colon carcinoma [14, 15, 16, 17, 18, 19, 20]. This study presents the results of the SLN procedure in six Dutch hospitals. The primary aim of this study is to test the accuracy and sensitivity of the SLN procedure in a multi-centre setting. Furthermore, we looked at upstaging and possible aberrant lymphatic drainage.
Materials and methods
This study was performed between May 2002 and May 2005 in five teaching hospitals and one university hospital. All procedures were supervised by one of the coordinating surgeons (Plukker, Braat). Only patients with histologically proven primary colon carcinoma were included in the study. Patients with distant metastases or gross lymph node involvement as shown by pre-operative examinations or palpation during surgery were excluded. The procedure was only performed when one of the study coordinators was available for supervision (Plukker, Braat, Kelder). The study was approved by the local scientific ethics committee, and all patients had given informed consent. Patients with rectal cancer were excluded from the study.
SLN mapping was carried out through an open procedure by injection of 1–3 ml Patent Blue with a tuberculin syringe and 29-gauge needle sub-serosally in four quadrants around the tumour. The sub-serosal injection was carried out before vascular ligation. Within 5 to 10 min after the blue dye injection, the SLN could be identified by following the blue-stained lymphatic vessels leading to the blue-stained SLN. These lymph nodes were tagged with a long suture. SLNs were defined as the first one to four blue-stained lymph nodes seen within the regional basin. After marking of the SLNs, routine resection was performed. If the SLN was found outside the normal lymphatic basin, we performed an extended resection. The tumour and all lymph nodes were examined according to standard guidelines . If the SLNs were negative after routine H&E staining, they were sectioned at 150-μm intervals and examined at three levels with H&E as well as immunohistochemistry on cytokeratins (CK7/8 or 18). Metastases between 0.2 and 2 mm were referred to as micrometastases. Metastases smaller than 0.2 mm were referred to as isolated tumour cells . Upstaging was defined as the presence of micrometastases or isolated tumour cells after immunohistochemistry (IHC) in patients with a negative lymph node status after H&E.
Mean number of lymph nodes
Mean number of SLN
Table 2 Results of multi-centre studies of the SLN procedure in colon cancer
We saw aberrant lymphatic drainage in three patients (4%). This percentage correlates with the literature [15, 18, 20]. In this study, none of these aberrant SLNs showed metastases. However, potentially, these aberrant SLNs are the only lymph nodes containing metastasis, as shown in a previous study . In an experimental situation, it seems justified to perform an extended resection in these cases. Further study should be performed to justify an extended resection in the daily practice.
Literature not clearly indicates how many nodes should be examined to accurately predict lymph node status [6, 7, 8, 23, 24]. One study showed that a colon specimen usually contains about 50 lymph nodes and that more than 70% of the lymph nodes containing metastases are smaller than 5 mm . It is also known that the prognosis in node-negative patients with colon carcinoma is better when more lymph nodes have been examined . Taking this into account, the pathologist takes only a sample of the lymphatic basin of a resected colon specimen, even when international guidelines are followed, which state that at least 12 lymph nodes are needed for adequate staging . The mean number of 11 lymph nodes in our study is not enough to predict lymph node status according to the international guideline. This fact could theoretically lower the chance to detect metastases in non-SLN and thus could lower the false-negative rate. However, we did not find any differences in false negative rates between the two hospitals with a mean number of nine and ten examined nodes (40 cases) and the hospitals with more than 12 examined nodes (29 cases). With regards to upstaging, most studies show an upstaging of 10–16% [15, 18, 19, 20]. However, they calculated upstaging by dividing the number of IHC-positive patients by the total number of patients (Fig. 1g/a, 9 of 69, 13% in our group). We think it is better to consider upstaging solely in the H&E node-negative group, as this is the group to be upstaged by IHC. Using this method, we find 18% upstaging in our series. In addition to this true upstaging, patients with a SLN as the only site of metastases could have been ‘possibly upstaged,’ as conventional pathological dissection of the mesentery might have missed this lymph node. The SLN procedure with patent blue might be able to improve adequacy of the lymph node examination by selecting the right lymph nodes, even small nodes less than 5mm, to be examined in depth by the pathologist. We found the SLN to be the single lymph node with metastasis in 15 (21%) of the patients (Fig. 1 f). ‘Possible upstaging’ might play a role here, but we cannot prove this.
As we believe that even isolated tumour cells are important for staging, we assigned patients with micrometastases or isolated tumour cells to the group of node-positive patients. It must be remarked, however, that these cases were also used for the calculation of upstaging. Our idea of the biological importance of micrometastases and isolated tumour cells is based on a recent meta-analysis that showed that micrometastases detected retrospectively by RT-PCR correlated better with overall survival than IHC and carried significant prognostic value .
Regarding the detection of micrometastases, two studies showed a high reliability of the SLN concept to predict micrometastases and/or isolated tumour cells also in non-SLNs. Therefore, it seems sufficient to perform IHC only on the SLN, while examining the non-SLNs with H&E [25, 26]. Prospective studies are needed to evaluate the potential benefit of systemic chemotherapy in patients with these micrometastases. A reliable SLN procedure might facilitate this intensive pathological examination by allowing focussed examination of only the SLN and thereby aid in a better patient selection for adjuvant therapy in the future.
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