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Page 12 of 16 De Iaco et al. Mini-invasive Surg 2020;4:63 I http://dx.doi.org/10.20517/2574-1225.2020.37

33.5% in thymic carcinomas and NETs, but these rates could be underestimated because lymphadenectomy
is rarely performed by most institutions [91-95] .

Two factors have been described to explain lymph node metastasis, namely WHO subtype and tumor size,
[92]
being both closely related to the biologic aggressiveness of the tumor [96,97] . Hwang et al. described lymph
node metastasis rate according to WHO histologic types as 5% for Type A, 1.6% for Type AB, 4.8% for Type
B1, 9.5% for Type B2, 10.7% for Type B3, and 31.8% for thymic carcinoma. They also found that lymph
node metastasis rate was higher in tumor larger than 6 cm. Moreover, most authors have reported lymph
node metastasis to be more frequent in tumors invading adjacent organs; these findings suggest lymph
node dissection to be performed at least in those patients undergoing en bloc resection of thymus and
neighboring organs for carcinomas and carcinoids [97,98] .

[98]
Park et al. suggested dissection of more than 10 lymph nodes to be enough for adequate staging. They
retrospectively reviewed 45 patients who underwent thymic resection for carcinoma; during the surgery,
they performed lymphadenectomy of a mean of 9.4 lymph nodes and divided the patients in four groups
according to the extension of lymph node dissection: no lymph node dissection (Nx), node-negative by < 10
nodes dissection (N0a), node-negative by > 10 nodes dissection (N0b), and node metastasis (N1). They
found that the five-year FFR rates were 33.3% in N1, 64.1% in N0a, 75% in Nx, and 90% in N0b, while the
five-year DFS rates were 33.3% in N1, 48.1% in N0a, 75% in Nx, and 90% in N0b.

Although no evidence has proved it yet, it is possible that surgeons with expertise in minimally invasive
lobectomy and lymphadenectomy for lung cancer may easily endorse the idea of nodal dissection, to be
performed at least in advanced thymomas involving neighboring structures, large masses, and thymic
carcinomas.

CONCLUSION
Radical en bloc thymectomy including the upper cervical poles and the surrounding mediastinal fat is the
gold standard treatment for non-MG thymoma and adequate margins are considered the most important
prognostic factors.

Open approaches remain the gold standard treatment, but minimally invasive techniques could be
effectively used in small, early-stages thymic masses, above all because, despite the shortage of studies,
the rate of radicality would seem to be slightly higher for minimally invasive techniques. Transcervical,
subxiphoid, thoracoscopic, and/or robotic approaches have been described and compared in many studies,
each having advantages and drawbacks. However, the lack of prospective randomized trials still gives
no answer about which approach should be better among the available ones. Moreover, the concept of
radicality should include pathological features of surgical removal (resection must involve the thymoma,
thymus, and mediastinal fat) and operation modalities: minimally invasive resection of a thymic neoplasm
does not require the use of rib retractor or the execution of sternotomy. The goal is to perform a complete
resection using a video monitor, and the service incision to remove the neoplasm must be large enough not
to damage the operating piece during extraction. Therefore, minimally invasive surgery is to be preferred to
open techniques not only in terms of radicality but also for the best postoperative performance (less pain
and aesthetic result).

Although several authors have proposed thymomectomy as a valid limited resection technique, appropriate
for patients with small and early-stages thymomas, still little evidence supports its oncological and long-
term advantages.

Finally, the role of lymphadenectomy of the mediastinum for thymic lesions has not been clarified, and
this surgical procedure has long been underperformed. Since WHO subtype, tumor size, and invasion of