Value of Immunohistochemistry in Gynecological Pathology
Moderator: Dr. W. Glenn McCluggage
Case 7 -
Vulvar Squamous Cell Carcinoma, Keratinizing Type, HPV Related
Dr. Jaume Ordi, Hospital Clinic,
27-year-old woman. 2 cm. vulvar exophytic tumor in the para clitoridal area.
Case 7 - Figure 1
The histologic examination showed a conventional invasive well-differentiated keratinising squamous
cell carcinoma. No intraepithelial component (VIN) was identified.
Immunohistochemical stains showed an intense positivity for p16. p53 was
negative in the tumor cells. High-risk HPV sequences (type 16) were identified using two different PCRs
(GP5/GP6+ and SPF10).
Diagnosis: Vulvar squamous cell carcinoma, keratinizing type, HPV related
Invasive vulvar squamous cell carcinoma (VSCC) accounts for more than 90% of malignant vulvar
neoplasms. Based on their etiopathogenesis, VSCCs have been divided into two groups with different
clinical and pathological features. One group expresses sequences of high-risk human papillomavirus
(HPV), whereas the other arises via independent-HPV pathways. The prognostic significance of these
pathological groups is still controversial.
Non-HPV-associated VSCCs, which account for two thirds of all VSCCs, arise in elderly women.
Histologically, these lesions are of the conventional keratinizing type and are frequently associated
with squamous cell hyperplasia and lichen sclerosus. In the last few years an infrequent variant of
vulvar intraepithelial neoplasia (VIN), the differentiated (simplex) type of VIN, has been described in
association with keratinizing VSCC. Non-HPV-associated VSCCs frequently show mutations of the tumor
suppressor gene p53. As a consequence p53 protein is frequently detected immunohistochemically in
keratinizing VSCC and differentiated (simplex) VIN3 due to cellular accumulation of the mutated abnormal
HPV-associated VSCCs account for approximately one third of all VSCCs. They are described as arising
in young women and are frequently associated with synchronous or metachronous HPV-positive tumors of the
uterine cervix, vagina or anus. HPV-associated VSCCs share risk factors with cervical carcinoma, such as
cigarette smoking, condylomas, and multiple sexual partners. Histologically, HPV-associated VSCCs are of
basaloid or warty type and arise from undifferentiated bowenoid or basaloid VIN. The malignant
transformation is mediated by inactivation of p53 and retinoblastoma by the viral gene products E6 and
E7. The inactivation of retinoblastoma results in an overexpression of p16.
Molecular detection of HPV sequences has been used to define both subgroups of vulvar carcinomas and
their precursors. Technical difficulties in routinely detecting and typing HPV in formalin-fixed,
paraffin-embedded tissues prevents its widespread use in many laboratories. As a consequence, pure
morphologic criteria are usually the only basis to classify HPV-positive and -negative VSCCs. However,
there is increasing evidence that some overlap exists between morphological types of VSCCs in terms of
their relationship to HPV. Thus, some conventional keratinizing VSCCs arising in young women are likely
to be HPV-positive, while some HPV-negative VSCCs show verruciform or poorly differentiated areas that
overlap with true warty or basaloid HPV-associated carcinomas.
Recent results by our group show that, as observed in the uterine cervix, an intense and diffuse
expression of p16 in a vulvar squamous cell carcinoma indicates a high-risk HPV-associated process, this
being irrespective of the histological type. p16 expression is detected both in the infiltrative areas
and in the associated intraepithelial lesions. Keratinizing VSCCs show, in contrast, a high frequency of
p53 expression, which contrasts with the almost constant negativity in HPV-positive premalignant and
malignant lesions. p16 and p53 tend to be mutually exclusive.
In our series, the sensitivity and specificity of p16 immunostaining to detect HPV-associated
carcinomas is higher than the sensitivity and specificity of histologic classification and those of p53
negative staining (Table 1). Thus, our results clearly indicate that p16 immunostaining can be a useful
tool to properly classify VSCC into HPV-associated or non-HPV-associated.
Table 1. Sensitivity, specificity, positive and negative predictive values
for the diagnosis of human papillomavirus-associated carcinoma of diffuse positivity for p16, negative
staining for p53 and basaloid or warty histology (from Santos et al, Am J Surg
Pathol 2006; in press).
| ||p16 (+++) ||p53 (-) ||basaloid/warty histology|
|Sensitivity ||100% ||93.8% ||62.5%|
|Specificity ||98.7% ||35.5% ||93.4%|
|Positive predictive value ||94.1% ||23.4% ||66.7%|
|Negative predictive value ||100% ||96.4% ||92.2%|
A striking finding in our series was the overlap observed between the histological types and the
association with HPV. Thus, more than one third of all HPV-positive VSCCs were of conventional
keratinizing type, whereas a small, but significant number of HPV-negative VSCCs showed basaloid or warty
features. This suggests that the proposed classification of VSCCs into basaloid, and warty, both
considered to be associated with HPV infection, and keratinizing, considered not to be associated with
HPV, has a limited reliability, and that histological analysis alone results in the misplacement of some
tumors in terms of their HPV relationship. This overlapping may also reflect a certain degree of
subjectivity in subclassifying the invasive component of VSCCs as referred by some authors. Thus,
although basaloid and warty carcinomas can generally be readily distinguished from keratinizing squamous
cell carcinomas or verrucous carcinomas, sometimes this distinction is difficult. These difficulties are
particularly challenging in the proper diagnosis of warty carcinoma, which can closely mimic keratinizing
or verrucous carcinoma, which is not related to HPV infection. Also, the presence of keratinization in
basaloid carcinomas can hinder the differential diagnosis with poorly differentiated keratinizing
squamous cell carcinomas. Moreover, some mixed basaloid-keratinizing squamous carcinomas that can pose
serious problems have been described. p16 immunostaining may represent thus, a much more reliable tool in
classifying VSCCs according to their relationship to HPV infection.
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