Squamous proliferations on the legs of women: Qualitative examination of histopathology, TP53 sequencing, and implications for diagnosis in a series of 30 cases

A pilot study of p53 immunohistochemistry in atypical squamous lesions, using a vulvar scoring system

BACKGROUND

Histopathologic overlap between cutaneous squamous cell carcinoma (cSCC) and its indolent mimics likely leads to the overdiagnosis of cSCC.

OBJECTIVE

To perform a pilot study of the p53 immunohistochemical scoring system developed on vulvar squamous lesions in cSCC.

METHODS

The consistency and reliability of p53 immunostaining using a scoring system developed on vulvar cases, as compared with TP53 genomic sequencing, was studied in an initial cohort of 28 cutaneous cases. p53 labeling was further assessed in an additional 63 cases of atypical squamous lesions, including 20 atypical squamous lesions classified by the authors as benign, 22 cases diagnosed as cSCC without high-risk features, and 21 cases of high-risk cSCC (cSCC-HR).

RESULTS

The concordance of p53 labeling and TP53 sequencing was 82.1%. Four positive patterns of p53 mutation were identified: basal, parabasal/diffuse, null, and cytoplasmic. p53 positivity in atypical, benign squamous lesions (10%) was significantly lower than that of low-risk cSCC (63.6%, p = 0.0004) or cSCC-HR (90.5%, p < 0.0001). p53 positivity in low-risk cSCC versus cSCC-HR was not statistically significant (p = 0.07).

CONCLUSION

p53 Labeling may be a helpful biomarker to support the diagnosis of cSCC and distinguish cSCC from atypical but benign mimics.

Cognitive bias in pathology, as exemplified in dermatopathology

Cognitive bias refers to human thinking patterns, as well as pitfalls, that are reproducible. Importantly, cognitive bias is not intentionally discriminatory and is necessary to properly interpret the world around us, including microscopic slides. Thus, it is a useful exercise to examine cognitive bias in pathology, as exemplified in dermatopathology.

Aberrant p16, p53 and Ki-67 immunohistochemistry staining patterns can distinguish solitary keratoacanthoma from cutaneous squamous cell carcinoma

Keratoacanthoma (KA) is widely considered a benign, usually self-resolving, neoplasm distinct from cutaneous squamous cell carcinoma (cSCC), while some consider KA to be indistinguishable from cSCC. Published studies indicate utility for p16, p53, Ki-67 immunostaining and elastic van Gieson (EVG) in the assessment of KA and cSCC. We compared clinical features and staining patterns for p16, p53, Ki-67 and EVG in fully excised KA, cSCC with KA-like features (cSCC-KAL) and other cSCC (cSCC-OTHER). Significant differences between KA, cSCC-KAL and cSCC-OTHER were found for head and neck location (20%, 86%, 84%), and duration <5 months (95%, 63%, 36%). KA shows both a mosaic pattern for p16 (>25-90% of neoplasm area) and peripheral graded pattern for p53 (up to 50% moderate and strong nuclear staining) in 92% compared with 0% of cSCC-KAL and 0% of cSCC-OTHER. In contrast, a highly aberrant pattern (usually null) for one or both p16 and p53, was present in 0% of KA, 83.8% of cSCC-KAL and 90.9% of cSCC-OTHER. Abnormal distribution of Ki-67 beyond the peripheral 1-3 cells was uncommon in KA (4.2%) and common in cSCC-KAL (67.6%) and cSCC-OTHER (88.4%). Moderate to striking entrapment of elastic and collagen fibres was present in the majority of KA (84%), cSCC-KAL (81%) and cSCC-OTHER (65%). KA are clinically distinct neoplasms typically of short duration occurring preferentially outside the head and neck and generally lacking aberrations of p16, p53 and Ki-67, compared with cSCC that have high rates of aberrant or highly aberrant p16, p53 and Ki-67, but EVG lacked specificity.

Squamous carcinogenesis: potential truncal mutations

Squamous carcinogenesis is incompletely understood, but more recent genetic studies support that the order of acquired mutations is important. This paper will review more recent genetic studies with an emphasis on the potential truncal mutations, mutations critical to the trunk of the cancer evolutionary tree, in actinic keratosis, squamous cell carcinoma in situ, cutaneous squamous cell carcinoma, keratoacanthoma, and keratoacanthoma-like squamous proliferation.

A clinical and biological review of keratoacanthoma

Keratoacanthoma (KA) is a common skin tumour that remains controversial regarding classification, epidemiology, diagnosis, prognosis and management. Classically, a KA manifests as a rapidly growing, well-differentiated, squamoid lesion with a predilection for sun-exposed sites in elderly people and a tendency to spontaneously regress. Historically, KAs have been considered a variant of cutaneous squamous cell carcinoma (cSCC) and are often reported as KA-type cSCC. However, the penchant for regression has led many to categorize KAs as biologically benign tumours with distinct pathophysiological mechanisms from malignant cSCC. The clinical and histopathological similarities between KA and cSCC, particularly the well-differentiated variant of cSCC, have made definitive differentiation difficult or impossible in many cases. The ambiguity between entities has led to the general recommendation for surgical excision of KAs to ensure a potentially malignant cSCC is not left untreated. This current standard creates unnecessary surgical morbidity and financial strain for patients, especially the at-risk elderly population. There have been no reports of death from a definitive KA to date, while cSCC has an approximate mortality rate of 1·5%. Reliably distinguishing cSCC from KA would shift management strategies for KAs towards less-invasive treatment modalities, prevent unnecessary surgical morbidity, and likely reduce associated healthcare costs. Herein, we review the pathophysiology and clinical characteristics of KA, and conclude on the balance of current evidence that KA is a benign lesion and distinct from cSCC.

Keratoacanthoma, committed stem cells and neoplastic aberrant infundibulogenesis integral to formulating a conceptual model for an infundibulocystic pathway to squamous cell carcinoma

Keratoacanthomas (KAs) are distinctive tumors that are defined by their clinical and histopathological features. Their relationship and distinction from squamous cell carcinoma (SCC), however, remain controversial. All cytogenic and immunohistochemical markers that have been applied in this quest have failed. A close relationship of KAs to hair follicles has been recognized. The descriptive term infundibulocystic or infundibular SCC was introduced to define a more broad-based pathway encompassing KAs. The follicular infundibulum roles in respect to neoplasia and wound healing are important elements in understanding the pathogenesis of KAs. Mouse models for KA have provided insights into the relationship of KA to follicles and SCCs. These advances and together with the diverse clinical and histopathological aspects of KA have contributed to the formulation of a conceptual pathway. The central element is that ultraviolet (UV)-mutated or activated committed infundibular stem cells are driven by the combination of a mutated oncogenic RAS pathway linked with the Wnt/beta-catenin pathway responsible for stem cell maintenance, hair follicle development, wound healing and driving KA proliferation and terminal keratinization. The existence and activation of this mutated pathway may form the basis of the paradoxical emergence of KAs and SCCs in patients receiving BRAF and PD-1 inhibitor therapy.

Cutaneous immunohistochemical staining pattern of p53β isoforms

p53 is considered the guardian of the genome and as such has numerous functions. The TP53 gene is the most commonly mutated gene in cancer, and yet the exact biological significance of such mutations remains unclear. There are at least 12 different isoforms of p53, and the complexity of the p53 pathway may be in part related to these isoforms. Prior research has often not teased out what isoforms of p53 are being studied, and there is evidence in the literature that p53 isoforms are expressed differently. In this paper, we document the staining pattern of p53β isoforms in the skin and correlate it with mutational status in a subgroup of squamous proliferations of the skin. p53β isoforms are present in the cytoplasm of the differentiated layer of the epidermis and hair follicles (granular layer, infundibular and isthmus-catagen). p53β isoforms are diffusely expressed within the cytoplasm of well-differentiated squamous tumours with tetramerisation (C-terminal) domain mutations in TP53 Our results lend support to p53β isoforms being a marker of differentiation in keratinocytes.