Use of proliferation rate, p53 staining and perforating elastic fibers in distinguishing keratoacanthoma from hypertrophic lichen planus: a pilot study

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.

Distinction Between Hypertrophic Lichen Planus and Squamous Cell Carcinoma Requires Clinicopathologic Correlation in Difficult Cases

ABSTRACT

Distinguishing hypertrophic lichen planus (HLP) and squamous cell carcinoma (SCC) can be diagnostically challenging because of overlapping clinical and histopathological features. This study characterizes histopathological features in HLP and SCC, assessing their utility in diagnosing atypical squamous proliferations. We compared 12 histopathological features of 15 HLP and 11 SCC biopsies from the lower extremities. We then reviewed 16 cases that were diagnosed as atypical squamous proliferations with differential diagnoses of HLP versus SCC. Clinical follow-up allowed for retrospective categorization of these difficult cases as HLP or SCC. HLP showed significant differences in hyperorthokeratosis (P = 0.04), wedge-shaped hypergranulosis (P = 0.0033), and irregular psoriasiform hyperplasia (P = 0.004), whereas parakeratosis (P = 0.001), solar elastosis (P = 0.001), deep extension (P = 0.02), and perforating elastic fibers (P = 0.0001) were significant for SCC. A scoring system based on these significant differences was devised to aid the classification of difficult cases. 56% of the difficult cases received an "indeterminate" score. A score favoring HLP had a sensitivity of 44% and a specificity of 71%. Although significant differences were identified between cases of definitive HLP and SCC, these histopathological features were unable to distinguish difficult cases, highlighting the need for clinicopathological correlation in patients with atypical squamous proliferations of the lower extremities. Many difficult cases had histologic features that could not be evaluated because of the superficial nature of the biopsy. Therefore, obtaining a deep wedge or punch biopsy may facilitate a diagnosis in cases with a differential diagnosis of HLP and SCC.

Lichen planus follicularis tumidus: Immunotyping of the inflammatory infiltrate with focus on plasmacytoid dendritic cells

Lichen planus follicularis tumidus (LPFT) is a rare clinicopathological variant of lichen planus (LP), clinically presenting with red-to-violaceous plaques studded with comedo-like lesions and keratin-filled milia-like cysts. Histopathologically, LPFT is characterized by cystically dilated follicular infundibula in the dermis, surrounded by a dense lichenoid lymphoid infiltrate with an associated interface reaction. We describe the clinicopathological features of an additional case of LPFT, focusing on the number and distribution of CD123(+) TCF4(+) plasmacytoid dendritic cells (pDCs). In our case, pDCs represented approximately 5% of the total inflammatory infiltrate, predominantly exhibiting a lichenoid distribution around the infundibula with no evidence of cluster formation, thus ruling out cutaneous lupus erythematosus. Our report is the first to describe the number and distribution of pDCs in LPFT. The results of our immunohistochemical analysis corroborate the notion that LPFT should be regarded as a rare variant of LP.