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Prevalence and Pattern of Lymph Node Metastasis in Malignant Pleural Mesothelioma

Monday, August 25, 2008

Source: Annals of Thoracic Surgery

Lymph node status is an important indication of disease spread and treatment prognosis for patients with pleural mesothelioma and peritoneal mesothelioma, just as it is for patients with other forms of cancer. Patients who present with lymph nodes that are negative for cancerous invasion are considered early stage patients and they typically respond to treatment in a more robust manner than do patients with “positive nodal status,” that is, patients whose disease has metastasized to their lymph nodes. Mesothelioma staging sees any indication of positive nodal status as increasing the staging diagnosis, but little is presently understood about the meaning of the nodal groups that do exhibit infiltration. The mediastinal lymph nodes are the nodes most likely to experience metastasis, but the hilar lymph nodes are also a common location of cancerous invasion and the question remains open if positive nodal status of both the mediastinal and the hilar nodes is indicative of a more advanced stage of the disease than is mediastinal metastases alone.

To answer this question, researchers from Egypt conducted a study in which they investigated the “prevalence and pattern” of lymph node metastases in a selected group of patients. Their research has recently been published in the Annals of Thoracic Surgery.

Overview of the Study

The researchers conducted a retrospective study of 53 patients with biopsy-proven malignant pleural mesothelioma. During treatment, each patient received a contract-enhanced CT scan of the chest and upper abdomen, as well as chest roentgenogram and ultrasound of the abdomen and pelvis. All patients underwent spirometry, while some patients received MRI and others underwent bone or brain CT if clinical analysis suggested it.

The study group was divided into two cohorts for analytical purposes. The first cohort, made up of 37 patients, did not receive pre-operative mediastinoscopy and each patient underwent a multimodality treatment protocol. The second cohort, made up of the remaining 16 patients, received preoperative staging assessments via mediastinoscopy. In this cohort, patients whose lymph nodes were negative for metastases underwent trimodal therapy using surgery, radiation and chemotherapy, while patients who demonstrated positive nodal status were excluded from the trimodal therapy.

All of the patients eligible for extrapleural pneumonectomy underwent EPP and during surgery, the physicians conducted lymph node dissection and sampling which revealed a patient’s true disease stage.

Results

There were 33 men in the study and 20 women. 34 patients presented with epithelial mesothelioma, while 16 presented with biphasic mesothelioma and 3 with sarcomatoid mesothelioma. Among the patients who did not receive preoperative staging assessments, 12 patients were subsequently identified as having mediastinal or hilar lymph node involvement. 11 patients were identified as having mediastinal metastases and 5 were identified with hilar metastases. However, of the latter group, four patients had both hilar and mediastinal involvement, while one patient was positive for hilar node involvement without concurrent mediastinal involvement, so the group figure for nodal involvement was set at 12. In the second group, 6 patients demonstrated nodal metastases. Mediastinoscopy revealed the nodal involvement in four of these cases, while two were discovered after surgery. All in all, 18 (34%) cases of lymph node metastases were uncovered in this study.

When analyzing the relationship between histological subtype, overall aggression and nodal infiltration, the researchers confirmed that the sarcomatoid and biphasic subtypes of the disease were more aggressive than the epitheloid subtype. They found that all patients whose disease had infiltrated their lungs presented with either sarcomatoid or biphasic mesothelioma. The researchers also found that this group of patients was more likely to demonstrate lymph node metastases than were patients with epitheloid mesothelioma. Of the 18 total cases with nodal metastases, 42% (8 cases) had sarcomatoid or mixed mesothelioma, while only 29.4% (10 cases) had epitheloid mesothelioma.

While nodal metastases are always indicative of a more advanced stage of the cancer, the authors conclude that differences in the nodes that were invaded must also be considered when staging. They state that the mediastinal lymph nodes should be considered the primary mesothelioma nodal station and indications of positive mediastinal lymph node status should be staged as N1 disease, while hilar metastases represent a more advanced cancer and should be recognized as N2 disease.

The authors also state that while mediastinoscopy is not a prefect diagnostic tool, it can be important for the preoperative staging of mesothelioma patients because it can reveal the presence of nodal metastases that PET or CT cannot. EBUS-TBNA represents the latest diagnostic advancement for the staging of pleural mesothelioma, but is not yet widely used, so until it becomes more commonly utilized, the authors state that PET, CT and mediastinoscopy should be the basic staging tools deployed in the diagnosis of mesothelioma.

Conclusion

The authors conclude their article with a call for revisions to the mesothelioma staging guidelines, as well as for more research into this topic. A number of previous studies have shown that early diagnosis of mesothelioma is an important indication for disease treatability, so improvements in the accurate diagnosis and staging of the disease will be helpful to many people whose lives have been touched by this difficult disease.

Labels: diagnosis, mesothelioma

posted by Belluck & Fox at 5:02 PM
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