2020-18 / May 4
(Contributor: Stephen Rohan)

The patient in his 40s presented with a complaint of a right testicular mass. Ultrasound revealed a 2.0 cm cystic mass. Serum tumor markers (HCG, AFP, LDH) were all normal. Positive immunohistochemical stains are shown. Additional stains performed (all negative) included CK5/6, calretinin, and OCT4.


1. What is the correct diagnosis?

a. Mesothelial hyperplasia

b. Malignant mesothelioma

c. Serous borderline tumor / atypical proliferative serous tumor of the para-testis

d. Metastatic carcinoma

e. Embryonal carcinoma

1. Serous borderline tumor / atypical proliferative serous tumor of the para-testis

The entire spectrum of ovarian-type epithelial tumors has been reported in the para-testicular area. The diagnostic criteria for these tumors are the same as they are for tumors primary to the gynectological tract. Serous borderline tumors (also known as atypical proliferative serous tumor) are the most common type of ovarian-type epithelial tumor to occur at this location.

From a treatment / prognostic perspective the most important differential diagnoses include invasive serous carcinoma, malignant mesothelioma, and germ cell tumor. Invasion in these tumors is excluded based on H&E morphology and generous sampling. Immunohistochemical stains are most helpful in excluding the other tumor types in the differential diagnosis. Based on the cases reported in the literature to date, serous borderline tumors of the para-testis have a good prognosis and are cured by radical orchiectomy.

1. McClure, RF, et al. Serous borderline tumor of the paratestis. Am J of Surg Pathol 2001; 25(3): 373-378.

Stephen Rohan, MD
Colorado Pathology Consultants, PC


Ovarian-type epithelial tumor, Serous borderline tumor, Atypical proliferative serous tumor