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13 May 2020 - Case of the Month #491

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Thanks to Drs. Stephanie J. Conrad and Ming Zhou, Tufts Medical Center and the Genitourinary Pathology Society (GUPS) for contributing this case and discussion.



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Case of the Month #491

Clinical history:
A 39 year old man presented with a painful, slowly enlarging left testicular mass. A left radical orchiectomy was performed.

Histopathology images:


What is your diagnosis?

Click here for diagnosis, test question and discussion:



Diagnosis: Adenomatoid tumor

Test question (answer at the end):
Which of the immunohistochemical stains, when positive, supports the diagnosis?

A. CD34
B. AFP
C. Calretinin
D. B72.3
E. Inhibin

Discussion:
The lesion arises in the paratesticular region. The testis showed normal spermatogenesis (not shown). On low power, the lesion is circumscribed and nonencapsulated with lymphoid aggregates at the periphery. The lesion has a varied growth pattern consisting of glands, tubules, cords, small nests and occasional single cells. The stroma is fibrous with lymphocytes dispersed throughout. On higher magnification the tubes, chords and cysts are formed and lined by cuboidal to flat epithelial cells with eosinophilic cytoplasm and cytoplasmic vacuoles. Some single cells with small cytoplasmic vacuoles resemble signet ring cells. Many cells lining the tubules and glands have vacuoles of considerable size, imparting a microcystic appearance. The nuclei are round and bland, lacking nucleoli; mitosis and necrosis are absent.

Adenomatoid tumors are rare, yet account for 30% of all paratesticular tumors. They are benign tumors of mesothelial origin. They may be intratesticular and infiltrate between testicular tubules, which should not be interpreted as evidence of malignancy. Key histological features include a circumscribed lesion, varied growth pattern, prominent lymphoid aggregates, vacuolated cytoplasm and lack of mitosis. Immunoreactivity for epithelial (AE1/AE3, 34betaE12) and mesothelial markers (WT1, D2-40, calretinin) supports the diagnosis.

Due to the wide spectrum of morphological patterns, the differential diagnosis for adenomatoid tumors is broad and includes primary and metastatic adenocarcinoma of testis, vascular tumors, malignant mesothelioma, germ cell tumors (especially yolk sac tumor), and other sex cord stroma tumors such as Leydig cell tumor and Sertoli cell tumor.

Rarely, malignant mesothelioma of the paratestis enters the differential diagnosis when the lesion is florid and extends into the testis. The presence of marked cytological atypia, increased mitosis, tumor necrosis and vascular invasion should raise the concern for mesothelioma; homozygous deletion of p16 supports this diagnosis.

When an adenomatoid tumor exhibits extensive cytoplasmic vacuolation, a yolk sac tumor may be suspected. Yolk sac tumors have more nuclear pleomorphism and lack the desmoplastic stroma seen in adenomatoid tumors. Additionally, yolk sac tumors stain positive for AFP and glypican 3, unlike adenomatoid tumors.

The dilated cystic and tubular spaces in adenomatoid tumors may be mistaken for a vascular lesion. However immunohistochemistry for vascular markers (CD34 and factor VIII) will be negative in adenomatoid tumors. Adenocarcinomas, both primary and metastatic, will stain positive for CEA and MOC31 / BerEP4, which are negative in adenomatoid tumors. Immunostains for B72.3 and inhibin are also negative in adenomatoid tumors.


IHC stain in this case:

Calretinin



References:
Clin Med Pathol 2009;2:17, WCRJ 2015;2:e606, Can Urol Assoc J 2015;9:133, Int J Surg Pathol 2011;19:838

Test question answer:
C. Calretinin