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De Iaco et al. Mini-invasive Surg 2020;4:63 I http://dx.doi.org/10.20517/2574-1225.2020.37 Page 11 of 16

study from the Chinese Alliance for Research in Thymoma database, retrospectively analyzed 1,047 patients
who underwent thymomectomy or thymectomy for early stages thymoma; they found a higher recurrence
rate in the thymomectomy group, especially for patients with Stage II thymomas (14.5% vs. 2.9%, P = 0.001).
[81]
Similarly, Nakagawa et al. , in their multicenter study from the JART database, retrospectively analyzed
1286 patients who underwent thymomectomy or thymectomy for early stages thymoma before and after
propensity score analysis; they found a higher recurrence rate in the thymomectomy group (2.1% vs. 0.41%,
P = 0.06).

[88]
Masaoka published an anecdotal study about his surgical experience in Osaka and Nagoya. In the first
experience, most of the 93 patients underwent simple thymomectomies, whereas a majority of patients in
the Nagoya series underwent extended thymectomies; in the early 1980s, simple thymomectomy was the
procedure of choice, later replaced by extended thymectomy. He found that overall survival rates of the
Nagoya series were superior to those of the Osaka one (87.1% vs. 66.7% for Stage I; 80.6% vs. 60.0% for
Stage II).

[89]
Voulaz et al. published the first study about 157 patients who underwent thymectomy or thymomectomy,
comparing for the first time long-term outcomes for advanced-stage thymomas and carcinomas, while
previous reports have focused only on early stages. They found that oncologic outcomes in terms of
disease-free survival rate of thymomectomy vs. thymectomy were superimposable and their median follow-
up was 77 months.

To date, there is no prospective study comparing the two approaches and the evidence is still sparse,
deriving from retrospective, single-institution, and small studies. The largest published analyses prove that
thymomectomy alone is not enough from an oncological point of view for early-stage thymoma. Moreover,
given the indolent behavior of these tumors, long-term follow-ups are needed to assess the real rates of
recurrence and the superiority of one technique to another.

LYMPHADENECTOMY
For many years, the role of lymphadenectomy of the mediastinum for thymic lesions has not been made
clear, and this surgical procedure has long been underperformed. Despite this, lymph node metastases have
proven to be a significant, independent, and adverse factor for FFR in patients with thymic carcinoma and
thymoma. To date, no clear guidelines are available regarding lymph node dissection and data from the
majority of studies show that lymph node sampling is not routinely performed during surgeries, except in
Japan where lymphadenectomy has traditionally been a part of the thymic resection.

The Masaoka staging system included N involvement in Stage IVb but made no distinction among the
[88]
different nodal stations . The eighth edition of tumor, node, and metastasis classification for thymic
tumors, instead, has classified nodal stations into anterior (N1) and deep (N2) regional nodes; their
involvement stage lesions as IVa or IVb disease .
[90]

Anterior mediastinal lymph nodes seem to be the primary drainage basin for thymic epithelial tumors and
lymphatic diffusion apparently spreads from the anterior to the deep nodes following a right route. This has
been determined based on frequency and pattern of metastasis in addition to anatomical location: nodal
metastases are located in the anterior mediastinum in 90% of thymomas and carcinoids and 70% of thymic
carcinomas .
[91]

The actual incidence of lymph node metastasis has not been well established. Historically, the prevalence
of lymph nodes involvement has been described ranging from 1.8% to 5.1% in thymomas and from 20% to