Primary Vulval Rhabdoid Tumor in an Adult: A Case Report, Immunohistochemical Profile and Literature Review

We report a rare case of primary vulval rhabdoid tumor in an adult. The diagnosis was confirmed using the recently emerging INI1/BAF47 immunostain. We also demonstrate the expression of ER and PR hormonal receptors by the tumor cells.


Introduction
Extrarenal malignant rhabdoid tumors (EMRTs) are rare and highly aggressive neoplasms. Although they are known to occur during infancy and childhood, their occurrence in adults is reported. EMRTs were described in various anatomical sites, and the use of INI1 immunostain has recently emerged as an important adjunct for identifying these tumors. An extensive online search of the literature revealed very few reported cases of EMRT of the vulva [1][2][3][4][5][6][7][8][9][10]. We hereby report another case and the first in which the INI1, ER, and PR immunostains were utilized.

Case Description
A 25-year-old Saudi female, who is medically free, presented to our emergency department complaining of a mass in the mons pubis. The mass was occasionally tender and had rapidly increased in size in two-week duration. No other complains or masses at other sites were reported. On clinical examination, an ill-defined soft mass was identified in the mons pubis, extending to the left inguinal area with a hyperemic overlying skin. Laboratory tests were within normal limits except for a mild leukocytosis. The clinical impression was of an abscess, and the patient was scheduled for surgery. A local excision of the mass was done, and the specimen was sent to the histopathology department. The patient was discharged on the next day of surgery.

Gross Findings.
Grossly, the specimen consisted of two irregular pieces of soft tissue. Both masses were partially encapsulated and measured 6 × 5 × 2 cm and 6.5 × 6 × 2.5 cm, respectively. The outer surface of both masses was irregular. Serial slicing of the masses revealed a heterogeneous cut surface with pale white and dark tan areas. Random sections from both masses were taken for histopathological examination.
A diagnosis of malignant rhabdoid tumor of the vulva was established. The patient was recalled once the histopathology report was signed out. A computed tomography scan (CT) of the head, chest, abdomen, and pelvis was performed and revealed no other tumor masses. Unfortunately, the patient failed to show for followup.

Discussion
We report a case of EMRT of the vulva in a 25-yearold female. The age of the patient, the site of the tumor, the clinical presentation, and the microscopic findings in our case were compatible with the 12 previously reported cases (Table 1) [1][2][3][4][5][6][7][8][9][10]. The IHC profile varied between cases, and the only universal finding was immunoreactivity to vimentin. Recently, INI1 immunostain has emerged as  an adjunct for identifying rhabdoid tumors and atypical rhabdoid/teratoid tumors (AT/RTs). INI1, encoded by the INI1/hSNF5/SMARCB1/BAF47 locus at 22q11.2, is a member of the SWI/SNF chromatin-remodeling complex, and it is normally expressed in all tissues [11,12]. The biallelic inactivation of this gene is characteristic to rhabdoid tumors of the kidney, EMRTs, and AT/RTs [11,12]. We have confirmed our diagnosis using the INI1/BAF47 antibody which showed universal loss of nuclear INI1 protein expression in all tumor cells. We have also studied the hormonal status of this tumor and found it to express both ER and PR receptors. This finding is compatible with its primary location in the vulva and has been previously reported in other vulval tumors [13].
Malignant rhabdoid tumor was originally described in the kidney as a variant of Wilms' tumor. In 1982, the first extrarenal malignant rhabdoid tumor was reported, and since then this entity was recognized at various anatomical sites including soft tissues, liver, prostate, thymus, skin, pelvis, heart, and central nervous system [14,15]. These tumors have a predilection to the pediatric age group though cases in adults were repeatedly recognized. The common microscopic feature is the "rhabdoid" cell of which the entire tumor is composed. These tumors usually coexpress vimentin and cytokeratin, and they do not retain the nuclear expression of INI1 protein. The prognosis of ERMT is generally poor, and their course tends to be aggressive. Although surgery is the first line of management, there is no consensus that exists regarding adjuvant therapies. Chemotherapy and radiotherapy did not show to be effective in controlling the recurrent or metastatic disease in all reported cases [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15].
In summary, vulval EMRTs are rare and aggressive neoplasms and should be considered in the differential diagnosis of any high-grade undifferentiated tumor at this site. Given that IHC is much more widely available than molecular tests, INI1/BAF47 immunostain represents the most useful, up to date ancillary technique to confirm this diagnosis. Although these tumors express ER and PR receptors, their response to antihormonal therapy is a remote possibility [13].