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Review
. 2021 Jan;38(1):50-61.
doi: 10.1053/j.semdp.2020.09.010. Epub 2020 Sep 25.

Molecular events in the pathogenesis of vulvar squamous cell carcinoma

Affiliations
Review

Molecular events in the pathogenesis of vulvar squamous cell carcinoma

Deyin Xing et al. Semin Diagn Pathol. 2021 Jan.

Abstract

Vulvar squamous cell carcinomas (VSCC), which constitute over 90% of vulvar malignancies in adults, are classifiable into 2 subgroups that are mostly clinicopathologically distinct, a classification that is fundamentally based whether or not the tumors are HPV-mediated. In this review, we aim to summarize the recent advances in the understanding of molecular events in the pathogenesis of VSCC, including common and targetable mutations, copy number alterations, epigenetics, noncoding RNAs, and tumor immune microenvironment, which may provide insight into the future management of the disease. These events show substantial differences between the 2 subgroups, although significant areas of overlap exist. Recurrent, driver mutations appear to be substantially more prevalent in HPV(-) VSCC. TP53 mutations are the most common somatic mutations in VSCC overall, and are notably predominant in the HPV(-) VSCC, where 30-88% show a mutation. TP53 mutations are associated with worse patient outcomes, and co-mutations between TP53 and either HRAS, PIK3CA or CDKN2A appear to define subsets with even worse outcomes. A wide variety of other somatic mutations have been identified, including a subset with different mutational frequencies between HPV(+) and HPV(-) VSCC. CDKN2A mutations are common, and have been identified in 21 to 55% of HPV(-) VSCC, and in 2 to 25% of HPV(+) VSCC. Hypermethylation of CDKN2A is the most frequently reported epigenetic alteration in VSCC and the expression of some microRNAs may be associated with patient outcomes. The PTEN/PI3K/AKT/mTOR pathway is commonly altered in HPV(+) VSCC, and is accordingly potentially targetable. HPV-positivity/p16 block expression by immunohistochemistry has been found to be an independent prognostic marker for improved survival in VSCC, and may have some predictive value in VSCC patients treated with definitive radiotherapy. 22-39.3% and 68% of VSCC show EGFR amplification and protein overexpression respectively, although the prognostic and predictive value of an EGFR alteration requires additional study. Recurrent chromosomal gains in VSCCs have been found at 1q, 2q, 3q, 4p, 5p, 7p, 8p, 8q, and 12q, and there may be differential patterns of alterations depending on HPV-status. At least one-third of VSCC patients may potentially benefit from immune checkpoint inhibition therapy, based on a high frequency of PD-L1 expression or amplification, or a high tumor mutational burden. Additional studies are ultimately required to better understand the global landscape of genetic and epigenetic alterations in VSCC, and to identify and test potential targets for clinical application.

Keywords: CDKN2A, Differentiated vulvar intraepithelial neoplasia (dVIN); High-grade squamous intraepithelial lesions (HSIL), Molecular events, Mutation, PI3K/AKT/mTOR, TP53, Vulvar squamous cell carcinoma (VSCC).

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Conflict of interest statement

Conflicts of Interest: The authors have disclosed that they have no significant relationships with, or financial interest in, any commercial companies pertaining to this article.

Figures

Figure 1.
Figure 1.
Two representative HPV-unrelated vulvar squamous cell carcinoma cases with TP53 mutation [3]. One tumor (A, H&E) harbors a TP53 p.Arg175His missense mutation. Consistent with this genotype, the tumor demonstrates aberrant/mutation-type p53 over-expression (B, strong and diffuse nuclear staining pattern). Another tumor (C, H&E) had a TP53 p.Gln165fs frameshift mutation that leads to synthesis of a truncated p53 protein. Thus, the tumor demonstrates aberrant/mutation-type complete loss of p53 expression (D) because the truncated protein cannot be recognized by the p53 antibody. A wild-type/normal pattern of p53 expression is seen in the stroma as an internal control.
Figure 2.
Figure 2.
Overview of the multistage, stepwise evolution of HPV-unrelated vulvar squamous cell carcinoma (VSCC). The HPV-independent pathway often, but not always, starts with lichen sclerosus, which can develop into differentiated vulvar intraepithelial neoplasia (dVIN), which is thought to be the precursor of HPV-unrelated VSCC. Genome-wide analysis has provided genetic and epigenetic evidence for a clonal relationship between lichen sclerosus, dVIN, and HPV-unrelated VSCC. TP53 somatic mutation and CDKN2A promoter methylation have been observed in all three lesions. Additional genetic (for example, somatic mutations of CDKN2A, NOTCH1, and HRAS) and epigenetic alterations (for example, promoter methylation of MGMT, RASSF2A, RARβ and IRF6) acquired in the each step facilitate the oncogenic process.
Figure 3.
Figure 3.
A representative HPV-related vulvar squamous cell carcinoma case with a wild-type TP53 [3]. The tumor displays a basaloid morphology with focal keratinization (A) and demonstrates strong and diffuse p63 (B) and p16 (C) expression with detected high-risk HPV by RNA in situ hybridization (D).
Figure 4.
Figure 4.
Overview of the multistage, stepwise evolution of HPV-related vulvar squamous cell carcinoma (VSCC). HPV infection leads to development of vulvar intraepithelial lesion 1 (VIN 1)/low-grade squamous intraepithelial lesion (LSIL). HPV E6 oncoprotein has the ability to neutralize the function of p53 and E7 oncoprotein binds and inactivates the tumor suppressor protein Rb. 20% of VIN 1/LSILs persist, of which half causes vulvar intraepithelial lesion 2–3 (VIN 2–3)/high-grade squamous intraepithelial lesions (HSILs). A small subset of VIN 2–3/HSILs develops into HPV-related VSCC. Additional genetic (for example, somatic mutations of PIK3CA, FGFR3, and FBXW7) and epigenetic alterations (for example, promoter methylation of SH3GL2 and Stratifin) acquired in the each step facilitate the oncogenic process.
Figure 5.
Figure 5.
Distribution of 7 mutations including TP53, CDKN2A, HRAS, PIK3CA, NOTCH1, and FGFR3, in HPV-unrelated (A) and HPV-related (B) VSCCs. The graph presents the results of the following seven studies: Xing et al. [3], Nooij et al. [28], Trietsch et al. [39], Weberpals et al. [27], Han et al. [36], Prieske et al. [10], and Zieba et al. [29]. HPV-unrelated VSCCs display relatively high somatic mutational frequencies in TP53, CDKN2A, HRAS, and NOTCH1 genes, whereas HPV-related VSCCs harbored more mutations in PIK3CA and FGFR3 genes.
Figure 6.
Figure 6.
Aberrant expression of PD-L1 in paired primary and metastatic VSCCs [3]. A representative primary vulvar SCC (A, H&E) shows PD-L1 expression with Combined Positive Score (CPS) approximately 50 (B); metastatic tumor (C, H&E) demonstrates increased PD-L1 expression with CPS of approximately 75 (D).

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