Background
Lung cancer is the second most common cancer, and most cases are diagnosed at advanced stages. The 5-year survival rate of lung cancer is less than 20%. Lung cancer in non-smokers appears to be a distinct disease caused by driver mutations that are different from the genetic changes observed in lung cancer in smokers. In western countries, rearrangements in the gene (
ALK) encoding anaplastic lymphoma receptor tyrosine kinase have been found in only 3–7% of lung adenocarcinomas; in contrast,
EGFR mutation is approximately 10–15%, more frequent than
ALK rearrangement [
1,
2]. Nevertheless, these two alterations appear to be mutually exclusive in patients [
3,
4], and only recent rare cases have shown concomitant alterations in
ALK and
EGFR [
5,
6].
Ovarian metastatic tumors derive from many sites. The common primary sites include gastrointestinal tract, pancreas, and gynecologic tract (the cervix and uterus) [
7]. However, lung carcinoma metastasis to the ovary is rarely reported. Reports of these metastatic tumors have included all major lung cancer histotypes, with small cell carcinomas comprising the largest proportion, followed by adenocarcinomas, large cell carcinomas and squamous cell carcinomas [
8]. As stated above, lung adenocarcinoma metastases to the ovary are rare, and the incidence is not yet clear. Lung metastasis to uncommon sites occurs in less than 5% of cases, with metastatic adenocarcinoma to the ovary occurring in only 0.07%. So the frequency of total lung tumor metastasis to the ovary is estimated to be less than 0.01% [
9]. More remarkably, although ovarian metastasis from lung carcinoma has an extremely low incidence,
ALK rearrangement in these patients has occasionally been reported [
10‐
17].
In the present study, we investigated 7 consecutive cases of lung adenocarcinoma metastasis to the ovary at our institute with cases-review in the literature. We obtained clinicopathological data regarding major molecular alterations for targeted therapy. To the best of our knowledge, this study is the largest panel of ovarian metastatic tumors from lung adenocarcinomas focusing on genetic alterations to date.
Discussion
The most common non-small cell lung cancer (NSCLC) metastatic sites are the brain [
21], followed by the bone and liver [
22]. All other organ metastases comprise less than 5% of cases, and thus, they may be defined as uncommon metastases. The anatomical sites in decreasing order of frequency are the soft tissue, kidney, pancreas, spleen, peritoneum, intestine, bone marrow, eye, ovary, thyroid, heart, breast, tonsil nasal cavity [
9], and gastric region [
23]. The total frequency of lung metastasis to the ovary is estimated to be less than 0.01% [
9]. Due to the paucity of reported cases, the clinicopathological features of these tumors remain unknown. To the best of our knowledge, this is the largest number of cases of ovarian metastasis from lung adenocarcinoma examined to date. Although the ovary is an uncommon metastatic site in the female reproductive tract, uterine cervix metastasis from lung adenocarcinoma harboring
ALK rearrangement has been reported [
24], as have concurrent cervix and breast metastases [
25]. In our cohort, the minority (19%) of ovarian metastatic tumors involved only one metastatic site, whereas the majority of ovarian metastatic tumors were concurrent with other metastatic sites (81%), especially the bone and brain.
Ovarian mucinous carcinoma accounts for only 3–4% of all primary tumors [
26], and most cases constitute metastatic tumors from diverse sites. As previously noted by Lee et al. [
27], metastatic tumors of the ovary tend to show bilateral masses. However, unilateral masses were common in our cohort of metastatic lung adenocarcinomas (11/16, 68.8%), in contrast to Krukenberg tumors with bilateral masses. This is consistent with unilateral ovarian metastasis in twelve of nineteen cases in Irving’s report [
8]. Furthermore, tumors greater than 10 cm in size tended to be primary ovarian tumors, but the mean size in the present study was 11 cm. These findings indicate that ovarian metastatic tumors from lung adenocarcinomas have distinct clinicopathological features compared with those from other organs, and some characteristics may result in misdiagnosis of primary ovarian tumors.
Metastatic mucinous carcinomas mainly include those of the gastrointestinal tract, pancreatic, and gynecologic organs [
27,
28]. Lung adenocarcinoma metastases to the ovary are extremely rare and comprise less than 0.01% of cases [
9]. Although metastatic ovarian tumors prior to the primary lung adenocarcinomas were not found in our cohort, 5 cases (16%) of ovarian tumors were reported prior to the lung carcinoma, including 1 adenocarcinoma [
8]. Hence, differentiating primary ovarian tumors from metastatic tumors is a major challenge, especially for mucinous ovarian carcinomas. A panel of immunohistochemical markers should be used for differential diagnosis. PAX8 is recognized as a sensitive marker of the gynecologic tract [
29], but it was absent in all 7 cases in our cohort. TTF-1 and Napsin A, which are commonly-used pulmonary-origin markers, are helpful in distinguishing these cases from cases of primary ovarian mucinous carcinoma [
30]. TTF-1 and Napsin A were expressed in all 7 cases, and metastatic lung adenocarcinoma was further supported with the negative results for PAX8, HNF-1β, ER and PR, and history of lung adenocarcinoma.
Dominant oncogenes in NSCLC are associated with different biological behaviors manifesting as distinct patterns of metastasis, and
ALK rearrangement predisposes to rare sites of pericardial and pleural disease [
31,
32]. Interestingly, in the present study, 11/16 (69%) cases harbored
ALK rearrangements in an unselected rare ovarian metastasis from a lung adenocarcinoma as the most frequent molecular alteration.
EML4-ALK fusion genes are predominantly observed in younger, nonsmoking/light smoking female populations, especially in East Asia. Histopathologically, this
ALK rearrangement in lung adenocarcinoma appears to promote the unique features of solid and/or signet ring cells [
33]. Other features have been found in cases with
ALK rearrangements, whereby mixed subtype adenocarcinomas were the most common subtype, followed by the acinar predominant subtype, papillary predominant subtype [
34], micropapillary and cribriform growth [
35,
36], bronchioloalveolar carcinoma (BAC) and low-grade endobronchial mucoepidermoid carcinoma. Rare casesof adenosquamous carcinoma and mucoepidermoid carcinoma has been reported [
35]. Although there is one reported case of ovarian metastatic lung adenocarcinoma with comprehensive solid and signet ring cells [
16], regrettably, there was no further genetic analysis of this case. Our results also indicated that the solid phenotype is highly suggestive of
ALK alteration, and 4/5 cases with solid features harbored
ALK rearrangement. However, the acinar pattern was slightly more common than was the solid pattern in patients with
ALK rearrangement (6 acinar vs. 5 solid), which is consistent with previous reports in which lung adenocarcinoma with
ALK rearrangement was likely to be related to acinar components [
37].
Notably, lung cancer with
ALK rearrangement represents only a small subset of NSCLC, but metastatic ovarian tumors were found to occur in most
ALK fusion-positive cases. Why the ovary is the favored site of these lung cancers is not known. In our cohort, the ALK protein was expressed in 4 cases (57%), and 100% concordance with the FISH results was observed. Most evidence demonstrates good correlation between the immunohistochemical staining of ALK (clone D5F3) and FISH [
38]. To reduce the economic burden, patients should be screened by
ALK immunohistochemistry to ensure whether they are suitable for targeted therapy. Notably, pleural metastatic tumors weakly express
ALK (clone D5F3), but 75% were positive for ALK rearrangement by FISH; therefore, the results of immunohistochemical and FISH may be inconsistent for distant metastases [
38].
Recently, Gupta R et al. demonstrated a decreased median survival rate for
ALK-positive tumors with uncommon sites of metastasis compared with common sites [
31]. However, only one patient with ovarian metastatic
ALK-positive tumors was reported in their paper (this was not reanalyzed in the current study due to lack of detail information). According to our data, slightly increased survival compared with triple-negative (no EGRF/KRAS/ALK alterations) and EGFR/KRAS mutation cases may be associated with uncommon metastatic ovary tumors with ALK rearrangement, though this difference was not statistically significant. As mentioned, patients with
ALK rearrangement have a better prognosis than do those with wild-type
EGFR [
39]. Hence, patients with
ALK rearrangement and uncommon sites of metastasis to the ovary may achieve better outcomes and longer survival times. Because of the paucity of ovarian metastasis from lung adenocarcinoma, longer follow-up times and more samples are needed for further research.
The
EGFR mutation is approximately 10–15%, more frequent than
ALK rearrangement [
1,
2]. Histologically, patients with
EGFR mutation more frequently display BAC or papillary components, but the incidence of solid features is lower than that in other patients [
40,
41]. One patient in our group with an
EGFR mutation in exon 19 (p.746-750del) showed the acinar subtype, which conformed to the morphological features, and the mutation was in concordance with that of the primary lung adenocarcinoma. According to previous reports, there is an approximate discordance rate of 16.2–27% between primary lung adenocarcinomas and corresponding metastases. One case showed L858R in a primary lung cancer but 2235-2249del in ovarian metastatic tumors [
42]. Because the responsiveness to
EGFR tyrosine kinase inhibitors tends to correlate with the
EGFR mutation status in metastatic lesions compared with primary tumors [
42,
43], metastatic tumors should be retested. Patients with rare
EGFR mutations in metastatic ovarian carcinomas are likely to have a worse prognosis than are those with tumors with
ALK rearrangement.
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