Histopathological spectrum of squamous cell carcinoma in horn cancer of cattle

Introduction

Squamous cell carcinoma (SCC) poses a significant health challenge within the Indian cattle population, leading to marked reductions in productivity and contributing to substantial economic losses within the agricultural and livestock sectors. As per the 20th Livestock Census (2019) [1] , India's total livestock population stands at 535.78 million, with bovinesincluding Cattle, Buffalo, Mithun, and Yak-constituting 302.79 million. This represents a 1% increase from the previous census, underlining the crucial role of cattle in India's agrarian economy. Among various neoplastic conditions affecting cattle, SCC stands out as a particularly prevalent and economically burdensome pathology, especially in indigenous Zebu cattle. The prolonged morbidity and associated mortality significantly impair the draught capabilities of affected animals. According to Udharwar et al. (2008) [8] , the overall incidence of neoplasms in Indian cattle is 53.5%, with SCC comprising approximately 41.46% of these cases. A notable manifestation of SCC occurs in the horn tissue, affecting nearly 1% of the Indian cattle population and accounting for over 80% of documented tumors in this region (Mukeshbhai et al., 2024) [6] . SCC originates from the stratified squamous epithelium of the skin and mucous membranes (Vegad, 2007) [10] . Though the precise etiology remains unclear, its development is understood to be multifactorial. Contributing factors include prolonged exposure to ultraviolet (UV) radiation, lack of skin pigmentation, chronic irritation due to yokes, horn painting, hormonal imbalances, sparse hair coverage, and viral agents such as papillomavirus. Compared to papillomatous tumors, SCC is more aggressive, characterized by uncontrolled cellular proliferation and infiltrative growth behavior.

Histopathologically, SCC in horn tissue reveals well-defined clusters or lobules of polyhedral squamous epithelial cells. These appear "prickly" due to prominent cell borders, with enlarged, pleomorphic nuclei. The lobules are separated by delicate connective tissue strands, and a defining microscopic feature is the presence of "epithelial pearls," which are concentrically layered keratin structures (Jaiswal et al., 2014) [4] . The tumor's histological grading plays a critical role in determining its biological behavior and clinical outcomes. As described by Gharagozlou et al., 2007 [3] well-differentiated SCC is marked by large islands of neoplastic epithelial cells with extensive keratinization and keratin pearl formation. Moderately differentiated SCC exhibits greater cellular pleomorphism, hyperchromatic nuclei, reduced keratinization, and early invasion. Poorly differentiated SCC is typified by pronounced cellular atypia, high mitotic activity, minimal keratin formation, and prominent inflammatory infiltration. These gradations influence tumor aggressiveness, invasiveness, and prognosis. Despite its clinical relevance and economic impact, limited studies have explored the histopathological diversity of SCC in bovine horn cancers. A detailed investigation into the tumor grading and histological subtypes is imperative for enhancing diagnostic accuracy and refining therapeutic interventions in veterinary oncology. Accordingly, this study aims to elucidate the histopathological spectrum of SCC in horn tissue of cattle, with particular emphasis on tumor differentiation and subtype classification. Through this characterization, the study seeks to contribute valuable insights into diagnosis, prognosis, and the formulation of effective management strategies for affected animals.

Materials and Methods

Sample Collection

A total of 48 samples of horn tissue suspected of squamous cell carcinoma (SCC) were collected from cattle presented at Veterinary Clinical Complex and Nearby Veterinary dispensaries between July 2024 and January 2025. The samples were obtained from cattle of different breeds, ages, and sexes to assess the histopathological spectrum of SCC. The affected horns tissue samples were collected following surgical excision. Each sample was labelled and preserved in 10% neutral buffered formalin for histopathological evaluation.

Histopathological Processing

The fixed tissue samples were processed using standard histopathological techniques. Briefly, tissues were dehydrated in ascending grades of ethanol, cleared in xylene, and embedded in paraffin wax. Serial sections of 4-5 μm thickness were cut using a rotary microtome and mounted on glass slides. The sections were then stained with Hematoxylin and Eosin (H&E) following the protocol described by Luna (1968) [5] to assess tumor architecture, cellular morphology, keratinization, and invasive patterns.

Histopathological Grading and Subtype Classification

The stained sections were examined under a light microscope at varying magnifications. SCC cases were graded into welldifferentiated (G0), moderately differentiated (G1), and poorly differentiated (G2) categories based on following [9] . Additionally, SCC subtypes, including pseudovascular SCC, desquamated SCC, verrucous SCC, and basaloid SCC, were identified based on specific histopathological features.

Results and Discussion

Squamous cell carcinoma (SCC) exhibited distinct histopathological characteristics that varied with the degree of differentiation, influencing tumor behavior and progression.

In well-differentiated SCC (G0), the neoplasm consisted of large clusters of squamous epithelial cells showing pronounced squamous differentiation. These cells formed numerous small keratin pearls comprising 4-5 layers of epithelial cells with a central homogeneous keratin core. Mitotic figures were relatively low, ranging from 6 to 13 per high-power field (hpf), primarily located around the keratin pearls. Cellular anaplasia was minimal, with cells retaining a typical squamous morphology and showing no pleomorphism.

The surrounding stroma displayed a dense inflammatory [3] in respect of grading of horn SCC in cattle.

Conclusion

Histopathological analysis of bovine horn SCC revealed a strong correlation between tumor differentiation and aggressiveness. Well-differentiated SCC (G0) showed organized keratinization, low mitotic activity, and a strong inflammatory response, indicating a less aggressive nature. The verrucous subtype, with bulbous epithelial projections, further reflected low-grade malignancy. Moderately differentiated SCC (G1) exhibited increased pleomorphism, higher mitotic rates, and early invasion. The pseudovascular variant, mimicking vascular channels, suggested a more aggressive behavior. Poorly differentiated SCC (G2) was the most malignant, with high mitotic activity, severe pleomorphism, and extensive necrosis. The desmoplastic subtype, marked by dense fibrous stroma, indicated high invasiveness. These findings highlight the importance of