In this pathologic review of primary tracheal squamous cell carcinoma, the largest series to date, we show that completeness of resection, involvement of the thyroid gland, and lymphatic invasion are histopathologic features with important prognostic value. Increasing depth of invasion into the tracheal wall is associated with a loss of histologic differentiation and lymphatic invasion. Although survival in well-differentiated carcinomas is higher, this difference is not significant and may be attributed to the higher incidence of lymphatic invasion in moderately and poorly differentiated carcinomas. Further, we observed that resected tracheal SCCs are mostly small tumors (median thickness 1.1 cm) and that tumor thickness within this range did not significantly affect prognosis. A possible explanation for this finding is that thickness may result from the exophitic portion of the tumor and thus is not conditioned on deeper invasion into the tracheal wall. A higher proportion of larger tumors, however, exhibit lymphatic invasion, a significant predictor of survival.
Surgical resection may lead to excellent survival even when the tumor violates the boundaries of the trachea and invades peritracheal fibroadipose tissue. To provide the best chances of survival, it is however important for the surgeon to achieve negative soft tissue resection margins. When faced with a tracheal SCC growing into the thyroid gland, our findings indicate that surgical resection should be applied to carefully selected patients, and palliative therapy may be considered when complete resection is otherwise compromised. Further, the pathologist reviewing SCC of the trachea should be aware of the importance of lymphatic invasion and specifically investigate the tumor for the presence of this feature.
There are some limitations to our study. We retrospectively analyzed large pathologic specimens of tracheal SCC, and only resected cases were included. Tumors growing into vital organs such as the heart or the great vessels and tumors involving long segments of airway judged unresectable were treated at the Massachusetts General Hospital but are not included in our study. We might have underestimated or misjudged the histologic characteristics, as only a limited number of representative slides for each case were available during histologic review; further, there were only five cases with invasion of the thyroid gland.
Tracheal SCC is a rare tumor, and few centers acquire proficiency in its surgical treatment. The dissemination of whatever prognostic information is available assumes therefore a greater importance. We confirm that lymphatic invasion predicts prognosis, while depth of invasion could not be correlated with survival, except for a marked decline when tumor was present at the resection margin or invaded the thyroid gland. We therefore conclude that even in cases where tumor invades peritracheal fibroadipose tissue, excellent survival can be achieved provided the patient undergoes surgical resection and the resection is complete. Positive resection margins in turn predict treatment failure. Our previous report showed that outcome in patients with unresected tumors is worse than in patients that underwent resection [5
], a finding supported here by the poor prognosis in patients with incomplete resection. Thus, tumor resectability, usually dictated by tumor length in the long axis of the airway and invasion of vital organs, may possibly be the single most important prognostic factor in this very distinct type of cancer.