Microscopic description:

Pathology revealed a proliferating spindle cells containing elongated, blunt-ended nuclei and eosinophilic fibrillar cytoplasm with scattered enlarged and irregular nuclei. The well-differentiated liposarcoma component, showed mature-appearing adipose tissue and fibrous bands with irregular nuclei. The sarcomatous component was positive for MDM2.  Spindle cells were positive for desmin and Ki67 in 10% of the tumor.

Ancillary testing:
  • Positive: Desmin, MDM2, Ki67 (10%). MDM2 immunohistochemical stain shows nuclear expression. This is a useful confirmatory marker for dedifferentiated liposarcoma.
  • Ae1/Ae3, S100, SOX10, Melan A

Molecular testing:
  • Overexpression of MDM2

The case was signed out a as a dedifferentiated para testicular liposarcoma, low grade, with MDM2 amplification. Testis showed no specific pathological changes and were negative for neoplasia. Histologic grade is 2. # Mitosis per 10 fields at 40x is 2. No necrosis was noted.

Discussion:

Paratesticular liposarcomas are rare malignant neoplasm showing adipocyte differentiation 1. Although rare, it is the most common sarcoma in para testicular tissue in adults comprising 12% of all liposarcomas 2.

The mean average age of presentation is 63 years. Liposarcoma may arise from the spermatic cord, tunica vaginalis, and rarely epididymis.

Most cases present with a longstanding growing, painless, inguinal, or scrotal mass, inguinal hernia, hydrocele, or hematocele 3 . The standard treatment for localized liposarcoma is radical orchiectomy with adequate negative margins is usually curative 4. However, the prognosis remains unfavorable with dedifferentiated liposarcoma type with metastasis potential. Local recurrence may occur after complete resection.

Well differentiated liposarcoma is characterized by the presence of amplification involving 12q13-q15. The 12q13-q15 region contains multiple genes implicated in the pathogenesis of liposarcoma, including MDM2, CDK4, HMGA2, TSPAN31, OS1, OS9, CHOP, STAT6 and GLI.

Gross examination mostly reveals a multilocular, tanned-yellow, large mass. The cut surface is firm, yellow tan to gray with areas of hemorrhage or necrosis in high grade tumors.

Common characteristic histologic features of well differentiated liposarcoma include atypical stromal cells and lipoblasts in the context of mature fat. Often with a prominent fibrotic component5. Multivacuolated lipoblasts are present but are few 5. Atypical adipocyte cells are large and have hyperchromatic nuclei with a bizarre, displaced nucleus (the nuclei of benign adipocyte are usually very thin and displaced to periphery of cell membrane). The adipocytes are often different in sizes and shapes 5.

The dedifferentiated liposarcoma histologic features includes a proliferation of atypical spindle cells containing elongated, blunt-ended nuclei and eosinophilic fibrillar cytoplasm with scattered enlarged and irregular nuclei. The well-differentiated liposarcoma component shows mature-appearing adipocytes and fibrous bands.

Most cases of dedifferentiated liposarcoma are positive for S100, desmin, actin, CDK4, MDM2, and p16 5. STAT6 has been reported in dedifferentiated liposarcoma 6.

References:

Montgomery E, Fisher C. Paratesticular liposarcoma: a clinicopathologic study. Am J Surg Pathol. 2003;27(1):40-47. doi:10.1097/00000478-200301000-00005

Vinayagam K, Hosamath V, Honnappa S, Rau AR. Paratesticular liposarcoma-masquerading as a testicular tumour. J Clin Diagn Res JCDR. 2014;8(2):165-166. doi:10.7860/JCDR/2014/8147.4045

Salas-Parra RD, Tavares LL, Gupta R, Silletti J, Shah A. Dedifferentiated liposarcoma of the scrotum. Case report and literature review. J Surg Case Rep. 2020;2020(9):rjaa342. doi:10.1093/jscr/rjaa342

Kodzo-Grey Venyo A, Deoleker M. Paratesticular liposarcoma of the spermatic cord: a case report and a review of the literature. West Afr J Med. 2011;30(6):447-452.

Kammerer-Jacquet S-F, Thierry S, Cabillic F, et al. Differential diagnosis of atypical lipomatous tumor/well-differentiated liposarcoma and dedifferentiated liposarcoma: utility of p16 in combination with MDM2 and CDK4 immunohistochemistry. Hum Pathol. 2017;59:34-40. doi:10.1016/j.humpath.2016.08.009

Doyle LA, Tao D, Mariño-Enríquez A. STAT6 is amplified in a subset of dedifferentiated liposarcoma. Mod Pathol Off J U S Can Acad Pathol Inc. 2014;27(9):1231-1237. doi:10.1038/modpathol.2013.247

CASE IMAGES