Metastatic Adenocarcinoma to the Breast arising from a Mediastinal Mature Teratoma with Somatic Malignancy: A Case Report with a Review of the Literature

Malignant transformation in mature teratomas, especially somatic-type malignancies, are extremely rare phenomena with few cases described in the literature. In the mediastinum, these lesions are often accompanied by metastases, ultimately unmasking them. We report an exceptional case of metastatic adenocarcinoma to the breast arising from a mediastinal mature teratoma with malignant transformation in a 31-year-old female. The patient initially presented with a breast lesion that was later diagnosed as either a triple negative ductal carcinoma or a metastatic adenocarcinoma of unknown origin. Extensive clinical workup and radiological imagining revealed an anterior mediastinal mass. Subsequent pathological examination of the mass showed a mature teratoma with malignant transformation equivalent to that found in the breast biopsy.


Conclusion
Mediastinal teratomas with malignant transformation (TMTs) are rare entities; however these tumors should be suspected in cases of suspicious mediastinal masses presenting with unusual clinical and radiological signs, such as metastasis of unknown primary origin. Pathological corroboration of extensive sampling and meticulous microscopic examination is crucial for the diagnosis in order to tailor subsequent treatment.

Background
Breast cancer accounts for more than 20% of all cancers affecting women (1). Conversely, metastases to the breast are rare and represent only 0.2% to 1.3% of mammary tumours (2)(3)(4). Among occult cancers, 30% are initially presented by breast metastasis (3)(4)(5). Imaging studies usually reveal a single wellde ned, occasionally speculated mass. The most common origin of these metastases are controlateral breast cancers, however, they can also arise from other neoplasms such as: carcinomas from the lung and ovary, melanomas, lymphomas and rhabdomyosarcomas particularly seen in young female patients (5,6). However, many other primitive sites have been reported (7).
Here we report a highly unusual case of metastatic adenocarcinoma to the breast in a young female arising from a mediastinal mature teratoma with malignant transformation.

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A previously healthy 31-year-old woman was referred to our cancer center following a recent discovery of a left breast lump. Her family history included an aunt who had died from ovarian cancer. Clinical examination revealed a nodular lesion located at the exterior upper quadrant of the left breast with no signs of in ammation or lymph node involvement. Routine hematological and biochemical investigations were unremarkable. Ultrasound study and mammography both showed a mass measuring 37 mm, classi ed as ACR4 (8). Biopsy of the mass revealed mammary parenchyma diffusely in ltrated by a moderately differentiated adenocarcinoma composed of variable sized glands in a discreetly brous stroma. These glands were lined by tall columnar epithelial cells displaying abundant eosinophilic cytoplasm, moderate atypia and rare mitoses. Some cells had intra-cytoplasmic mucin vacuoles ( Figures   1 and 2). The initial diagnosis proposed was a triple negative grade 1 invasive ductal carcinoma according to the modi ed Scarff-Bloom-Richardson classi cation system (9).
Consequent imaging by Computed Tomography revealed a well-de ned cystic anterior mediastinal mass with central necrosis, measuring about 10 cm and compressing adjacent anatomical structures. It also showed atelectasis, pulmonary and pleural thickening, multiple pulmonary nodules as well as regional lymphadenopathy.
Scintigraphy revealed multiple bone foci at the levels of L3, S1 and S2 and at the level of the 6th intercostal rib. Subsequent biopsy of the mediastinal mass revealed a moderately differentiated adenocarcinoma similar in morphology to that found in the breast biopsy. Interestingly, the immunohistochemical study showed a strong positivity for CK8/18 and CK7, a focal positivity for CEA and a mitotic index of 60%. All other immunostains including CK20, CDX2 and breast tissue markers were negative. Based on these ndings, a left anterior thoracotomy was performed to remove the mediastinal lesion.
On gross examination, the resected tumor measured 12 x 10 x 7 cm and weighed 99 g. It was well demarcated with no obvious signs of rupture. No de nite capsule or lung parenchyma were identi ed. The external surface had a glistened variegated appearance with alternating yellowish and congested areas. On sectioning, the mass was unilocular with a predominantly smooth wall and contained grumous material with hair.
Multiple thickened bourgeon areas measuring up to 1.5 cm associated with small yellowish colored granules were discovered inside the wall and on its interior surface. No papillary excrescences were found.
Microscopically, the cystic wall consisted of brocollagenous tissue lined by cuboidal and/or tall columnar mucin secreting epithelium with areas of minimal chronic in ammation and vascular congestion ( Figure 5). On sectioning of the thickened areas, mature elements of all three germ layers were found: -mesodermal derivatives such as adipose tissue, cartilage, and muscle bundles, -endodermal derivatives such as gastrointestinal tract tissue and ciliated bronchial tissue -and ectodermal derivatives such as strati ed squamous epithelium and sebaceous glands.
There were no immature teratomatous elements or other germ cell components associated. Furthermore, we noted multiple foci of atypical cells, arranged in groups or glands and surrounded by a reactive brous stroma. These cells contained abundant eosinophilic cytoplasm, sometimes with intracytoplasmic vacuoles and displayed a moderate degree of pleomorphism and atypia ( Figure 5). The immunohistochemical pro le was similar to that found in the breast biopsy and showed a positivity for cytokeratines, BerEP4 and CDX2, suggesting a digestive origin (Table 1).
A nal diagnosis of a mature teratoma with somatic-type malignant transformation, most likely an adenocarcinoma, with secondary breast metastasis was concluded.
The patient's postoperative course was uneventful and she was subsequently discharged. Unfortunately, the patient died a few months later.

Discussion And Conclusion
Triple-negative ductal carcinomas account for only 15% of mammary tumours but are responsible for a disproportionate number of deaths. In fact, these tumours are most often of high grade; low grades (or grade I) represent only 9.8 to 15.1% of these cases (10,11). Due to the overall rarity of this type of tumour, it is necessary to be cautious when establishing this diagnosis by thoroughly eliminating all other differentials, including metastasis. This case reports a metastatic adenocarcinoma to the breast in a young female arising from a mediastinal mature teratoma with somatic-type malignant transformation.
According to the most recent World Health Organization de nition, a teratoma with somatic-type malignancy is a teratoma containing one or more components of a non-germ cell malignant tumour, which may be a sarcoma or a carcinoma. These tumours represent 10 to 20% of all mediastinal GCTs with somatic-type malignancies (12). Histologically, it seems that the malignant component is often carcinomatous (13,14) but this somatic-type only represents 37% of all GCTs with somatic-type malignancies (15). These tumours mostly always occur in males (12), between the ages of 20 to 40 years; however a few cases concerning females have been reported in the literature, mainly as case reports (14,(16)(17)(18)(19)(20)(21)(22).
Same clinical features are also used to classify these tumours into two categories: TMTs induced by chemotherapy and/or irradiation and naturally occurring TMTs (14,16,18). Most reported cases have been from the former group, chie y occurring in young patients with an initial presentation of a malignant germ cell tumour. On the other hand, naturally occurring TMTs in the mediastinum are extremely rare and occur in older patients in the context of mature teratomas of long standing duration, generally with good prognoses (14,16). In our case, the malignant transformation most likely occurred naturally due to the absence of chemotherapy or radiation exposure. Contrarily, the breast metastasis demonstrates an aggressive nature to this tumour. To our knowledge, this is the rst reported case of a mediastinal TMT unmasked by breast metastasis.
TMTs should be suspect under certain clinical and radiological presentations such as: a voluminous mediastinal tumour measuring at least 10 cm in size (14) , adhesion to surrounding structures with or without invasion, local wall thickening with fatless solid areas and a contrast-enhancing capsule with a rough and uneven internal surface (13,22).
These non-germ cell malignancies are postulated to originate either from totipotential germ cells differentiating to somatic type cells or from pre-existing mature teratoma elements to non-germ cell malignancy (14,20,22). Molecular studies have shown an isochromosome 12p (i[12p]) genotype with no clearly de ned consequence in carcinogenesis, that is shared by both the somatic-type malignancy and its associated germ cell tumor component (12). The latter hypothesis is favored by the nding that "pure" mature mediastinal teratomas show no chromosome 12 abnormalities while a shared i(12p) abnormality is characteristic of teratomas that are clonally related with somatic type malignancies.
Interestingly, the majority of somatic-type malignancies do not immunohistochemistraly express PLAP, AFP, beta-hCG, or CD30, which are normally expressed in GCTs, but rather stain like their counterparts found elsewhere in the body. Cytokeratin immunostains, such as CK7 and CK 20, can be used to distinguish adenocarcinomas from other types of malignancies (21).
According to the literature, prognosis is poor compared to other GCTs, and depends mainly on surgical resection which is currently the recommended treatment. Other factors include, the primary tumor site and its margins, the type of transformed histology and the number of prior chemotherapy regimens before the development of TMT (23). Due to its rarity, the treatment of these tumors does not have a standardised chemotherapy protocol. However, adapted chemotherapy based on the TMT somatic malignant component is hypothesized to improve the overall outcome of these patients (13,(24)(25)(26).    Immunohistochemical stains on the breast biopsy. A) CK7+ strongly and diffusely positive. B) CK20 negative. C) Triple negative (PR-, RE-and HER2-).