December 2021 — Genitourinary Pathology

A 32-year-old man presented with a 2.8 cm testicular tumor. On gross examination, a hemorrhagic and ill-defined nodular area with a friable cut surface within the testicular tissue was noted. The surface of the tunica vaginalis was smooth and unremarkable except for the area where the hemorrhagic nodule was present.

Figure 1: ER
Figure 2: PAX8
Figure 3: Serous 1
Figure 4: Serous 2
Figure 5: Serous 3

Based on the history and photomicrographs, which one of the following diagnoses is correct?

  • Postpubertal-type teratoma
  • Adenocarcinoma of the rete testis
  • Mesothelioma
  • Serous borderline tumor

The correct answer is ...

Serous borderline tumor

Our case demonstrates a neoplasm with branching papillary architecture associated with cystic spaces. The tumor is lined by stratified serous-type epithelium with mild to moderate atypia and psammomatous calcifications. There is no stromal invasion. The neoplastic cells are positive for PAX8, WT1, and ER, which support the diagnosis of a serous borderline tumor.

The differential diagnosis includes mesothelioma, which can show microcystic and micropapillary patterns as seen in a serous borderline tumor. However, the overall immunophenotype rules out this possibility.

Another important differential diagnosis is teratoma, but other teratomatous components are not present. Also, no morphological evidence of germ cell neoplasia in-situ (GCNIS) was identified in the background seminiferous tubules, and this was supported by the absence of staining for OCT3/4.

Adenocarcinoma of the rete testes is a high-grade malignancy arising from the rete testis in the hilar region. These tumors show solid, tubular, or papillary patterns with clear stromal invasion, which is not evident in our case. Importantly, these tumors can be positive for PAX8; however, unlike serous borderline tumors, these tumors lack ER positivity.

Serous borderline tumors of testes are rare, and in one study, only 5 such cases were identified among 146 paratesticular and rete testis tumors.(1) Serous tumors of the testes, although rare, are the most common subtype of mullerian epithelial tumors and can show the same spectrum of benign, borderline, and invasive carcinomas as seen in the ovary.(2)

Serous borderline tumor of the testes are frequently located at paratesticular sites. However, intratesticular tumors can also be seen as in the case highlighted herein. These tumors are rare and have an indolent clinical course. Stromal invasion should be ruled out, as it carries adverse prognostic significance.(3)


  1. Appendageal tumors and tumor-like lesions of the testis and paratestis: a 32-year experience at a single institution.
  2. Geramizadeh B, Farzaneh MR, Pakbaz S, Zeighami S. Testicular papillary serous cystadenocarcinoma: a rare case report and review of the literature. Rare Tumors. 2011;3(4):e44. doi:10.4081/rt.2011.e44
  3. AMAR S. IBRAHIM, CHENG LI and MOHAMMAD S. AL-JAFARI Borderline Serous Papillary Tumour of the Testis: A Case Report and Review of the Literature Anticancer Research. November 2012, 32 (11) 5011-5013.

Rabia Zafar, M.D.

Fellow, Surgical Pathology
Mayo Clinic

Sounak Gupta, M.B.B.S., Ph.D.

Senior Associate Consultant, Anatomic Pathology
Mayo Clinic
Assistant Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

MCL Education

This post was developed by our Education and Technical Publications Team.