CASE OF THE WEEK
2021-40/October 4
Contributors: Andrew Hall, Jasreman Dhillon
A 61 year old male developed a scrotal mass which on gross examination revealed a 2.8 x 2.1 x 1.5 cm soft, multilocular cystic mass with white-yellow semi-translucent gelatinous contents
Quiz
1. What is the correct diagnosis?
a. Epithelioid mesothelioma
b. Papillary serous carcinoma
c. Yolk sac tumor
d. Embryonal Carcinoma
e. Adenocarcinoma of rete testis
2. What immunohistochemical stain results support this diagnosis?
a. SALL4-, CD30-, Calretinin+, WT1+
b. P16+, CEA+, Calretinin-, WT1+
c. SALL4+, AFP+, CDX2+, CD30-
d. SALL4+, CD30+, AFP-, CDX2-
e. PAX8+, MOC31+, SALL4-, CD30
3. What molecular test result supports this diagnosis?
a. BAP1 loss
b. MTAP retention
c. BRAF mutation
d. Isochrome 12p
e. CDK2NA amplification
1. a
2. a
3. a
Epithelioid Mesothelioma
Mesothelioma of the tunica vaginalis of the testis (paratesticular mesothelioma) is an uncommon, often fatal, paratesticular tumor. (1) The reported age of patients ranges from 12 to 84 years with an average of 55 years. Asbestos exposure believed to account for approximately 30-40% of cases. (1) On gross examination, mesothelioma of the tunica vaginalis often presents with multiple friable nodules along a hydrocele sac, hernia sac, or the peritoneum. It may invade into the tunica albuginea, testis, epididymis, and spermatic cord. (1)
Microscopically, mesotheliomas can present as epithelioid, mesenchymal, or mixed/biphasic. (2) Epithelial is most common morphology with growth patterns including papillary, tubulopapillary, glandular (well differentiated) or solid (poorly differentiated). Rarely, sarcomatoid or desmoplastic types can occur. The tumor cells in epithelioid mesothelioma are cuboidal with mild to moderate pleomorphism and often with prominent nucleoli. (1) Features of malignancy include high grade nuclear atypia, brisk mitosis, and infiltrative growth. (2) The immunohistochemical profile of mesothelioma of the testis is similar to mesothelioma elsewhere. Positive mesothelioma markers include calretinin, WT1, CK 5/6, and D2-40. A panel of immunohistochemical markers including two mesothelial markers and two epithelial markers is generally recommended. (3, 4)
A broad differential diagnosis should be considered prior to diagnosing mesothelioma of the tunica vaginalis. Papillary serous carcinoma of the tunica vaginalis may show morphologic overlap with mesothelioma. By immunohistochemistry, it is positive for Ck AE1/3, S100, EMA, and CEA. (1) Papillary pattern of yolk sac tumor (YST) can mimic papillary mesothelioma. Location of the tumor is important to distinguish the two entities. YST presents as a mass within the testicular parenchyma whereas mesothelioma is para-testicular in location. Immunohistochemical stains are helpful in distinguishing YST (SALL4, AFP, glypican-3, CDX2) from mesothelioma (calretinin, WT1, and D2-40). (1) Adenocarcinoma of the rete testis has papillary, tubulopapillary, and solid growth patterns with marked nuclear pleomorphism, apoptosis, mitosis, significant desmoplasia, and necrosis. Of note is the morphologic transition from non-neoplastic rete to adenocarcinoma with the presence of in-situ carcinoma. It is positive for cytokeratin, CEA, EMA, MOC31, CK7, BerEP4, and PAX8 and negative for mesothelial markers. (1)
Ancillary studies to support the diagnosis of mesothelioma include fluorescent in situ hybridization (FISH) which may show homozygous deletion of 9p21 which harbors the p16 gene or loss of BAP1. These findings are specific but not entirely sensitive for mesothelioma. (3)
1. Cheng L., Mackebbabm G, T,m & Bostwick, D. G. Urologic Surgical Pathology. Philadelphia, Elsevier, 2020. pp. 762-771, 828-829, 850-852
2. Vimercati L, Cavone D, Delfino MC, De Maria L, Caputi A, Ferri GM, Serio G. Asbestos exposure and malignant mesothelioma of the tunica vaginalis testis: a systematic review and the experience of the Apulia (southern Italy) mesothelioma register. Environmental Health (2019) 18:78 (B)
3. Husain AN, Colby TV, Ordonez NG, Allen TC et al. Guidelines for pathologic diagnosis of malignant mesothelioma.2017 Update of the consensus state from the International Mesothelioma Interest Group. Archives of Pathology Laboratory Medicine 2018.vol 142
4. Chapel DB, Schulte JJ, Hussain AN, Krausz T. Application of immunohistochemistry in diagnosis and management of malignant mesothelioma. Transl Lung Cancer Res 2020;(Suppl 1):S3-S27
Andrew Hall, Jasreman Dhillon
Moffitt Cancer Center, Tampa, FL
Testis
Mesothelioma, paratesticular, testis