Histologic mimics of perineural invasion

Unraveling the Mysteries of Perineural Invasion in Benign and Malignant Conditions

Perineural invasion (PNI) is defined as the dissemination of neoplastic cells within the perineural space. PNI can be a strong indicator of malignancy and is linked to poor prognosis and adverse outcomes in various malignant neoplasms; nevertheless, it can also be seen in benign pathologic conditions. In this review article, we discuss various signaling pathways and neurotrophic factors implicated in the development and progression of PNI. We also describe the methodology, benefits, and limitations of different in vitro, ex vivo, and in vivo models of PNI. The spectrum of presentation for PNI can range from diffuse spread within large nerves ("named" nerves) all the way through localized spread into unnamed microscopic nerves. Therefore, the clinical significance of PNI is related to its extent rather than its mere presence or absence. In this article, we discuss the guidelines for the identification and quantification of PNI in different malignant neoplasms based on the College of American Pathologists (CAP) and World Health Organization (WHO) recommendations. We also describe benign pathologic conditions and neoplasms demonstrating PNI and potential mimics of PNI. Finally, we explore avenues for the future development of targeted therapy options via modulation of signaling pathways involved in PNI.

Review of Perineural Invasion in Keratinocyte Carcinomas

Perineural invasion is an infiltrative process of peripheral nerves by the primary neoplasm within the immediate vicinity. Aggressive forms of keratinocyte carcinomas, such as basal cell and squamous cell carcinomas, may feature perineural invasion, which is often associated with tumor recurrence and poorer prognosis. Diagnosis requires a high clinical suspicion. Imaging and histopathology are used to assess for extent of disease while surgical excision with complete circumferential peripheral and margin assessment is the treatment goal. However, there is still significant uncertainty about adjuvant chemotherapy and definitive management guidelines. Here, we summarize the current understanding of this complex pathogenic process, the clinical presentation, and the significance of perineural inflammation. We also discuss the recommendations about staging, prognosis, adjuvant radiotherapy, and general guidelines for managing keratinocyte carcinomas with perineural invasion. A better understanding of perineural invasion is essential to improve diagnosis, tailor interventions, and mitigate patient morbidity and mortality.

Reparative Perineural Hyperplasia in the Gastric Wall: A Histologic Mimic of Perineural Invasion

Reparative perineural hyperplasia is an incidental and probably underreported reactive histologic finding thus far only reported in the setting of healing wounds or adjacent to a dermatofibroma in cutaneous specimens. It is characterized by a focal concentric proliferation of cytologically bland spindled perineurial cells and is hence considered a benign histologic mimic of neoplastic perineural invasion. Thus, it may present a diagnostic pitfall and we therefore consider it as a valuable entity to be aware of. To the best of our knowledge, this brief case report is the first to convey that reparative perineural hyperplasia may also occur in the gastrointestinal tract. It may therefore be a ubiquitous reactive histological phenomenon relating to previous surgical or traumatic wounds in various sites, that is, outside the thus far established setting of skin reexcision specimens.

Basal cell carcinoma with perineural invasion: A prospective study examining subtype, tumor surface diameter, invasion depth, and anatomic site in 3005 consecutive cases

BACKGROUND

Basal cell carcinoma (BCC) may present with or without perineural invasion (PNI). We reviewed BCC for PNI by subtype, microscopic tumor surface diameter, invasion depth, and anatomic site.

METHOD

Consecutive excisions were prospectively collected in an Australian center 2016-2018.

RESULTS

Total cases were 3005 including 40 with PNI: 28 in males, 12 in females. Superficial and nodular subtypes had no PNI. As the percentage tumor mass of infiltrative BCC increased beyond 90% the presence of PNI substantially escalated (OR7.0). Comparing PNI absent or present the respective maximum mean tumor microscopic surface diameters ranged from (95%CI [9.6-10.0] P < .001) to 11.2 mm (95%CI [9.4-13.0] P = .59). Respective maximum mean invasion depths were from 1.0 mm (95%CI [0.98-1.05] P < .001) to 2.3 mm (95%CI [1.8-2.7] P < .001). Respective maximum mean invasion depths were from 1.0 mm (95%CI [0.98-1.05] P < .001) to 2.3 mm (95%CI [1.8-2.7] P < .001) to 2.3 mm (95%CI[1.8-2.7] P < .001). Males recorded most PNI on the scalp, followed by cheek and chin. Patients with more than two BCC cases had a greater proportional PNI risk (OR3.7). Mean PNI nerve diameters were 0.06 mm² (males) and 0.03 mm² (females).

CONCLUSION

Increases in percentage infiltrative subtype within the tumor mass, microscopic tumor diameter, tumor invasion depth, and BCC cases per patient all recorded more PNI. Minimum invasion depths with PNI were 1.0 mm on males (nose) and 1.0 mm females (forehead).

Perineural Pseudoinvasion: An Unusual Phenomenon in Nonmalignancies

Perineural invasion (PNI) is characterized as tumoral or nontumoral cells invading in or around the nerves. The neural invasion is considered as a histopathologic characteristic for malignancy and is considered a mechanism for its spread. Both of these patterns usually portend a poor prognosis and very often are markers to prompt additional treatment. There are also some nonmalignancies representing PNI, including benign neoplasms, mimicking lesions, and disorders, such as chronic pancreatitis and endometriosis. The previously recommended terms are PNI, spread, or infiltration. To distinguish PNI in malignancies from that in nonmalignancies, we propose the term "perineural pseudoinvasion" to convey their nonmalignant behavior. Despite the low prevalence, awareness of this benign pseudoinvasion is necessary to avoid aggressive treatment and its misdiagnosis with malignancies. We conducted a systematic search in PubMed and Scopus databases up to December 2015 to find articles reporting PNI in nonmalignancies. After screening, 63 articles were identified as relevant. There were also 2 review articles discussing PNI in nonmalignancies. We aim to present an overview of the perineural pseudoinvasion and to discuss the previously published review articles.

Reexcision Perineural Invasion and Epithelial Sheath Neuroma Possibly on a Spectrum of Postinjury Reactive Hyperplasia Mediated by IL-6

Epithelial sheath neuroma is a rarely recognized but established entity in the medical literature. First described in 2000 by Requena et al, there have only been 7 published cases to date, mostly in female patients and presenting as symptomatic solitary lesions on the back without a known history of trauma. In 2006, Beer et al described and reviewed a dozen cases in which epithelial sheath neuroma-like features were seen in the advent of a surgical procedure, which was termed "re-excision perineural invasion" and attributed to possible eccrine duct implantation during surgery. Our case is a 66-year-old male patient who underwent an excision of a melanocytic neoplasm in which a reactive epithelial sheath neuroma was incidentally discovered in the excision specimen, adjacent to the biopsy site cicatrix. Histologically, there was benign cutaneous nerve hyperplasia with a proliferation of squamous epithelium in intimate apposition to the nerve bundles in the superficial dermis. We postulate that the process active in the formation of re-excision perineural invasion is the same as in epithelial sheath neuroma and that minor trauma not appreciable on histologic examination is responsible in the latter entity. We performed IL-6 staining and documented that IL-6 was upregulated at the interface of the nerve and reactive epithelium, but was absent in nerves distant from the site of surgery, suggesting that IL-6 may be essential to the lesion's development. The recognition of reactive epithelial sheath neuroma including the subcategory of re-excision perineural invasion is crucial for the dermatopathologist to prevent mislabeling this reactive entity as a perineural squamous cell carcinoma, which has clinical consequences for the patient such as wider re-excision and radiation treatment. Additionally, we have identified a potential pathophysiologic basis for this lesion.

Neurotrophin Receptors and Perineural Invasion: Analyses in Select Lineage-Unrelated Cutaneous Malignancies With a Propensity for Perineural Invasion

In this chapter, we parse the literature on neurotrophins that have been implicated in the pathogenesis of perineural invasion (PNI) in select lineage-unrelated malignancies. We also detail evidence linking neurotrophins and their receptors (TrkA, RET, p75NGFR, and NCAM) to the pathogenesis of PNI in desmoplastic melanoma and cutaneous squamous cell carcinoma-both malignancies with an established propensity for PNI. Lastly, the clinical potential of neurotrophins as receptors for targeted therapies is explored.

Perineural growth of benign cutaneous sweat gland tumors: a hitherto unrecognized phenomenon unassociated with malignancy

BACKGROUND

Cutaneous intraneural reactive epithelial proliferations mimicking malignancy include epithelial sheath neuroma, re-excision perineural invasion and reactive neuroepithelial aggregates. Nevertheless, intraneural growth of benign sweat gland tumors has not been reported before.

AIMS

To report a predominantly intraneural proliferation of morphologically bland sweat gland tumors, describe their clinicopathological features and correlate them with survival.

RESULTS

We analyzed a spiradenoma and a hidradenoma with a prominent intraneural growth, occurring on the back of the 19-year-old woman and on the arm of the 53-year-old woman. Both lesions presented as a painful and slightly raised papule. After complete excision, an uneventful clinical course was observed during the follow-up period of 52 and 54 months. Pathologically, the most striking feature was an almost exclusive intraneural growth within the peripheral nerves of the deep dermis and subcutis.

CONCLUSION

We report for the first time the predominantly intraneural growth of benign sweat gland tumors. Although their histogenesis is unknown, perineural displacement due to previous surgery or trauma, as well as development from intraneural embryological epithelial remnants remains possibilities. Long-term follow-up of our patients suggests that intraneural growth of otherwise bland sweat gland tumors does not signify malignancy. Complete excision appears to be sufficient treatment procedure.

Perineural invasion in cutaneous squamous cell carcinoma: role of immunohistochemistry, anatomical site, and the high-affinity nerve growth factor receptor TrkA

Perineural invasion (PNI) has been recently added to the American Joint Committee on Cancer cutaneous squamous cell carcinoma (cSCC) staging criteria as a high-risk tumor characteristic and is purportedly more common in cSCCs of the head and neck (H&N). Expression of the high-affinity nerve growth factor receptor TrkA has been shown to be associated with PNI in noncutaneous neoplasms. Given this, we sought to ascertain the incidence of PNI in cSCCs using double immunostaining (DIS) and to investigate PNI's relationship with TrkA and established histopathologic prognosticators. Fifty-seven cSCCs from the H&N and 53 from non-H&N areas were immunohistochemically analyzed for PNI (DIS with S-100 and p63) and TrkA expression. Comparing H&N versus non-H&N areas, using hematoxylin and eosin, PNI was detected in 11% versus 6% cases, respectively, and, using DIS, in 23% versus 15%, respectively, with significant disagreement between both methods (κ = 0.47; P = .002). There was a 2.33-fold increase in PNI detection with DIS compared to hematoxylin and eosin (95% confidence interval, 1.12-4.87; P = .02). TrkA expression was 1.96 times more frequently observed in cSCCs from the H&N compared to those from non-H&N areas (P = .01). Regardless of site, TrkA expression was associated with decreased degree of differentiation (odds ratio, 6.46; P = .0006) and high-risk morphologic variants (odds ratio, 6.53; P = .002) but not significantly associated with PNI (P = .33). Increased PNI detection with DIS underscores the adjunctive utility of immunohistochemistry in microstaging. Significantly more common TrkA expression in cSCCs of the H&N argues in favor of heterogeneity among SCCs from different anatomical sites.

Management of squamous cell and basal cell carcinomas of the head and neck with perineural invasion

Perineural invasion (PNI) occurring in non-melanoma skin cancers (NMSC) is associated with an increased risk of locoregional recurrence and reduced disease-free survival. This necessitates early and accurate diagnosis, appropriate risk-stratification and a clear management strategy. The diagnosis of PNI is based on careful clinical assessment, imaging and histopathology. Surgery, preferably with margin control, and definitive or adjuvant radiotherapy (ART) are established treatment strategies for PNI. Clinical uncertainty remains over the role of ART in incidental PNI. This review synthesises current literature to ascertain which clinicopathological features impart a higher risk to individuals with PNI in NMSC, in order to provide treatment algorithms, including the identification of patient subsets that are most likely to benefit from ART. This includes those with extratumoural PNI, involvement of larger-calibre nerves, tumour invasion beyond dermis, recurrent tumour or diffuse intratumoural spread. Patients with clinical PNI may be optimally managed by a multidisciplinary head and neck cancer service that is best placed to offer skull base surgery and intensity-modulated radiation therapy (IMRT). The management options presented are stratified by histological subtype and a new classification of PNI into low-risk, medium-risk and high-risk groups.

Dual S-100-AE1/3 Immunohistochemistry to Detect Perineural Invasion in Nonmelanoma Skin Cancers

Background. Perineural invasion (PNI) is an adverse prognostic histologic finding and increases the risk of local recurrence and metastasis. Objective. We aimed to determine if dual immunohistochemical (IHC) staining with S-100 and AE1/3 would increase the detection of PNI on nonmelanoma skin cancers (NMSCs). Methods. We collected 45 specimens of NMSCs in which there was clinical suspicion for PNI. Two dermatopathologists independently reviewed the tumors for the unequivocal presence of PNI. Results. Unequivocal PNI was present on 10 of the 45 tumors by H&E staining and on 15 of the 45 tumors by IHC staining. Large nerves (>0.1 mm) were involved in 3 of 10 H&E-stained cases and 3 of 15 IHC-stained cases, with 2 of the 4 cases demonstrating large nerve involvement with both staining methods. Of the 8 cases of PNI detected only on IHC, 7 were small nerves (≤0.1 mm). Limitations. All cases were selected because they were clinically suspicious for PNI, and this may be considered selection bias. Conclusions. PNI detection may be increased using dual S-100 and AE1/3 staining, but the majority of additional cases detected were small nerves. The clinical significance, given the small size of the involved nerves, is unclear.

Histopathological features of clinical perineural invasion of cutaneous squamous cell carcinoma of the head and neck and the potential implications for treatment

BACKGROUND

Nonmelanoma skin cancer (NMSC) with perineural invasion (PNI) is most commonly seen in cutaneous squamous cell carcinoma of the head and neck (SCCHN). The cranial nerves are a conduit for skin cancer to reach the brainstem.

METHODS

The histopathological features of 51 tissue specimens from 49 patients with cutaneous SCCHN and clinical PNI were assessed with consecutive transverse and longitudinal sections.

RESULTS

No skip lesions were identified. Tumor spread was contiguous in all specimens. No tumor spread into the perineural space from surrounding or adjacent tumor was seen. Proximal large cranial nerves showed epineural involvement in 3.9% in areas with large tumor bulk, extensive PNI, and intraneural invasion.

CONCLUSION

Perineural tumor spread in cutaneous SCCHN was contiguous and no skip lesions were evident in nerve specimens assessed in this series. Spread beyond cranial nerve perineurium was uncommon, reflecting its multilayer barrier function at this level. These findings may have treatment implications.

Mohs frozen tissue sections in comparison to similar paraffin-embedded tissue sections in identifying perineural tumor invasion in cutaneous squamous cell carcinoma

BACKGROUND

Perineural invasion (PNInv) in cutaneous squamous cell carcinoma (cSCC) increases the risk of recurrence, possibly because of suboptimal identification on frozen or paraffin-embedded tissue sections. Perineural inflammation (PNInf) may portend PNInv.

OBJECTIVE

We sought to correlate identification of PNInv and PNInf in hematoxylin-eosin-stained Mohs frozen sections with PNInv and PNInf identified in similarly oriented paraffin-embedded sections obtained in cases of cSCC.

METHODS

We reviewed same patient Mohs frozen and paraffin-embedded tissue sections for all patients presenting within a 2-year period to our Mohs micrographic surgical unit for removal of cSCC with PNInv or PNInf identified on either type of tissue section.

RESULTS

Of 537 patients undergoing surgical resection of cSCC, 21 (3.9%) had either PNInv (n = 11) or PNInf (n = 10) on frozen sections. PNInv on Mohs frozen sections was identified in 11 cases and confirmed on paraffin-embedded sections in 9 cases (82%). Paraffin-embedded sections failed to identify PNInv present in Mohs frozen sections in two (2/11), or 18% of cases. PNInf on Mohs frozen sections was confirmed on paraffin-embedded sections in 3 cases (30%), but PNInv was identified in 5 cases (50%).

LIMITATIONS

Our results are a retrospective case review from a specific time period by one institution. Furthermore, it is impossible to compare identical tissue specimens using two sequential tissue processing techniques.

CONCLUSION

PNInv can be accurately identified with Mohs frozen sections. PNInf on Mohs frozen sections suggests the presence of PNInv and requires further histologic investigation.