Squamous cell carcinoma transformation in mature cystic teratoma of the ovary: a systematic review

Background 0.17–2% of mature cystic teratoma of the ovary (MCTO) undergo malignant transformation, of which 80% are squamous cell carcinoma (SCC) transformation in MCTO. We aim to investigate the clinical characteristics and treatment of SCC transformation in MCTO Methods We systematically searched PubMed database and individual patient data about SCC transformation in MCTO were extracted. The published cases were combined with 6 cases of SCC transformation in MCTO from Qilu Hospital, Shandong University. Results The incidence of SCC transformation in MCTO was 0.3%. A total of 435 cases of SCC transformation in MCTO were enrolled in the analysis. The mean age of diagnosis was 53.5 (range 19–87) years old. The most common clinical manifestations were abdominal pain (47.3%) and abdominal mass (26.0%). StageI,II, III and IV accounted for 50.0, 18.8, 26.8 and 4.4% of all cases, respectively. Patients with stage I had significantly better prognosis than stage II, III and IV patients (P < 0.01). Hysterectomy can improve overall survival (P < 0.01). For patients younger than 45 years old with stageIA orIC, there was no difference in mortality between fertility-sparing and radical surgery (P = 1.00). Adjuvant chemotherapy can improve survival in patients with advanced stage (P = 0.02), and chemotherapy with platinum was related to better prognosis (P = 0.02). Conclusion SCC transformation in MCTO is a rare malignancy mainly occurs in older age. FIGO stage is an independent prognostic factor. Hysterectomy and platinum-based chemotherapy are associated with better survival. Fertility-sparing surgery is feasible for young patients with early stage. Electronic supplementary material The online version of this article (10.1186/s12885-019-5393-y) contains supplementary material, which is available to authorized users.


Background
Mature cystic teratoma of the ovary (MCTO) may occur in 10-20% of women during their lifetime [1]. The biological behavior of MCTO is benign, while 0.17-2% of MCTO may undergo malignant transformation [2]. There are various histological types of malignant transformation such as squamous cell carcinoma (SCC), adenocarcinoma, small cell carcinoma, sarcoma, malignant melanoma and mixed histology [3]. Among them SCC transformation in MCTO is most common, accounting for 80% of all malignant transformation [4].
The clinical manifestations of SCC transformation in MCTO are not specific. Tumor of early stage is often detected accidentally during physical examination or postoperative pathological examination [5], while palpable mass, bloating and abdominal pain are often present in advanced stage [6,7]. Acute abdomen may occur due to tumor torsion or rupture [8]. Moreover, preoperative imaging investigation and laboratory tests are not specific, either.  Large-scale clinical prospective study is not feasible because of the low incidence of SCC transformation in MCTO and the published cases are scattered, and the optimal treatment for SCC transformation in MCTO remains unclear [9]. Some doctors hold the idea that since SCC originates from epithelium so its treatment should follow principles that of epithelial ovarian cancer [10,11], some believe that the treatment should refer to SCC of other sites [12], and some suggest that since the malignancy presents on the basis of MCTO, which is a kind of ovarian germ cell tumors, the treatment can refer to that of ovarian germ cell malignancy. However, the surgical principle and postoperative adjuvant therapy of epithelial ovarian cancer, ovarian germ cell tumors and squamous cell carcinoma are different [13]. So it is of great importance to find out the most effective treatment.

Methods
We searched PubMed database with key words of "squamous cell carcinoma of mature cystic teratoma ovary", "malignant transformation mature teratoma ovary", "second tumor teratoma", "malignant dermoid cyst ovary", "MCTO squamous cell carcinoma", "SCC in MCTO", "mature cystic teratoma malignant". Cases of SCC transformation in MCTO published from January 1977 to October 2016 were included. Only cases with specific histology, invasive behavior and available individual patient data were included (Additional file 1: Figure S1). The MCTO cases of Qilu hospital between January 2005 and October 2016 were reviewed and 6 cases SCC transformation in MCTO were included in this study.
Clinicopathologic information, including age, tumor size, symptoms, stage, histological grade, surgical approach, adjuvant therapy, survival status and follow-up time were collected and analyzed. We used SPSS (version 21.0, for Windows) for statistical analysis. Data analysis was performed with descriptive statistics, chi-square test, Kaplan-Meier plots with Log-rank test, univariate and multivariate Cox proportional hazards regression model. A two-tailed P < 0.05 value was defined as statistically significant.

Retrospective chart review
From January 2005 to October 2016, there were 1836 MCTO cases in Qilu Hospital, Shandong University, 6 cases of them were SCC transformation in MCTO, accounting for 0.3% of all MCTO cases. Mean age of the 6   Table 2. Imaging investigation indicated cystic-solid mass with blood flow signal and enhancement. Grossly, the tumor consisted of cystic and solid components. There were typical components of MCTO such as hair, oil, sebaceous glands and epidermis. Microscopically, there were increased layers of squamous epithelium, disorderly arranged cells, squamous cells with atypia, irregular nuclei and necrosis (Fig. 1). All 6 cases were positive staining for p63, negative staining for p16, moderate to strong positive staining for Ki67 and alteration in p53. Detailed immunohistochemical panel is listed in Table 3 and Fig. 1.
As for treatment, hysterectomy can reduce death risk (P < 0.01) ( Table 6, Fig. 2b) whereas lymphadenectomy did not improve survival. Omentectomy did not improve survival with univariant analysis, while after adjusted with International Federation of Gynecology and Obstetrics (FIGO) stage, omentectomy was associated with better prognosis (P = 0.04) ( Table 6). 24 of the 51 patients younger than 45 years old with stageIA orIC underwent fertility-sparing surgery. There was no difference in mortality between fertility-sparing and radical surgery (P = 1.00).
Efficacy of postoperative adjuvant therapy was analyzed in a subgroup of SCC transformation in MCTO with stage II, III and IV. Adjuvant chemotherapy can improve survival in patients with advanced stage (P = 0.02) ( Table 7, Fig. 2c), and chemotherapy with platinum was related to better prognosis compared with other drugs (P = 0.02) ( Table 8, Fig. 2d). However, radiotherapy and chemoradiotherapy did not improve survival (Table 7).

Discussion
SCC transformation in MCTO is the most common malignant transformation of MCTO [4] and is also the most common cause of SCC of the ovary [9,104]. SCC transformation in MCTO may be a continuous process of squamous metaplasia, atypical hyperplasia, carcinoma in situ, interstitial infiltration and invasive carcinoma [14,105]. The mean age of MCTO patients without   [19,70], suggesting that unmanaged MCTO may undergo malignant transformation. SCC transformation in MCTO may be associated with high-risk human papilloma virus (HPV) infection [15], and alterations in p53 and p16 may be involved in the process of malignant transformation [16,17,106]. A recent next-generation sequencing analysis indicated that TP53 mutation was detected in 80% of SCC transformation in MCTO cases and mutation in TP53 correlated with better prognosis. PIK3CA and CDKN2A were altered in 52 and 44% cases, respectively [107]. In this study, 50% of cases are diagnosed in FIGO stage I. The proportion of stage I is much higher than that of all ovarian cancer, which is 15% [108]. More SCC transformation in MCTO cases can be detected in early stage because the malignant component originates from epithelium of preexistent MCTO [14], which is a gradual process, and is often found unexpectedly after resection of adnexal mass [1]. The same as epithelial ovarian cancer, FIGO stage is an independent prognostic factor for SCC transformation in MCTO. In this study, the 5-year survival rate of stage I patients is 85%, while in patients with stage II, III, the 5-year survival rate is less than 50%. So early detection is of great value and can improve the prognosis of SCC transformation in MCTO.
Comprehensive staging surgery is the standard treatment for ovarian cancer. Hysterectomy and omentectomy appear to improve survival of SCC transformation in MCTO, while lymph node dissection does not affect overall survival in our analysis. This observation suggests that local dissemination is an important metastasis manner of SCC transformation in MCTO. The cases included in this study are retrospective and are from multiple medical centers. What's more, some cases do not point out the exact scope of lymph node dissection. Since lymph node dissection is part of comprehensive staging surgery, we are in favor of performing lymphadenectomy despite the negative result in this study.
For patients with epithelial ovarian cancer in stages IA/IC, unilateral salpingo-oophorectomy is an optional treatment. For patients with malignant ovarian germ cell tumors, regardless of stage, fertility-sparing surgery can be done and after delivery a comprehensive operation should be conducted [13]. Our study suggests that for SCC transformation in MCTO, it is safe and feasible to perform fertility-sparing surgery in patients younger than 45 years of age old with stage IA/IC. There are cases of successful pregnancies after fertility-sparing surgery [57,74,83].
The recommend initial chemotherapy regimen for ovarian germ cell tumor and for epithelial ovarian cancer is bleomycin/etoposide/cisplatin (BEP) and paclitaxel/ carboplatin (TC), respectively. Currently there is no recognized first-line adjuvant therapy for SCC transformation in MCTO, though chemotherapy can improve prognosis of patients with SCC transformation in MCTO of advanced stage. Hackethal et al. suggest that chemotherapy with alkylating agents is related to better prognosis in patients with SCC transformation in  Cox proportional hazard regression model analysis MCTO [109]. However, in our study with the analysis of patients of stage II, III and IV, alkylating agents did not promote overall survival compared with others. We recommend individualized and integrated treatment based on platinum-based chemotherapy.
The histology of SCC transformation in MCTO is squamous cell carcinoma and genetic study indicates that SCC transformation in MCTO has features in common with other SCC [107], which are often sensitive to radiotherapy. However, our results suggested that radiotherapy does not improve prognosis of SCC transformation in MCTO. Whenever applied, doctors should pay attention to complications of radiotherapy [110].
This study has some limitations. Firstly, since the analysis is mostly based on review on published data, we cannot avoid the publication bias. Secondly, although preoperative detection of SCC transformation in MCTO is of great value, in our study we do not conduct the analysis because only a few papers reported the imaging features and serum markers [111,112]. The size of invasive component, which is possibly related to prognosis, is not available due to the retrospective study design. Moreover, few publications report cycles of chemotherapy, thus we do not investigate the optimal course of treatment. We recommend presentation of such information whenever reporting cases. Lastly, our results should be treated with caution, as the included studies span a prolonged time period (~40 years) during which changes in medical and therapeutic strategies may have changed.

Conclusions
SCC transformation in MCTO is a rare malignancy mainly occurs in older age. Early detection is important for better prognosis. Hysterectomy and platinum-based chemotherapy are associated with better survival. Fertility-sparing surgery is feasible for young patients with early stage. Due to the retrospective study design and limited data available, the results should be interpreted with caution. More reports are in need to elucidate the biology of SCC transformation in MCTO.

Additional file
Additional file 1: Figure S1. The flow chart of study selection and case inclusion. Table S1.

Availability of data and materials
The datasets analyzed during this study are accessible in the PubMed repositories. Data of cases from our institution are available in Table 2.
Authors' contributions CL and QZ contributed equally to this work. CL, QZ and BK conceived and designed this study. CL and QZ performed the literature search and study selection. CL, QZ, CQ and ZZ collected all data. SZ, RD and CS performed the immunohistochemistry and summarized the data. CL and QZ contributed to the data analysis and interpretation of results. CL drafted the manuscript. QZ and BK revised the manuscript. CL, QZ, SZ, RD, CS, CQ, ZZ, XY, and BK approved the final version of the manuscript to be published.

Ethics approval and consent to participate
The study was approved by the Ethics Committees of Qilu Hospital, Shandong University. Written informed consent form for publication will be available for every study participant.

Consent for publication
Written informed consent was obtained from the patients.