Squamous Cell Carcinoma – Diagnosis and Treatment

Squamous cell carcinoma (SCC) is frequently diagnosed in equids, with a reported incidence between 7% and 37% of skin tumours. It is the most common tumour of the penis and prepuce, followed by papilloma, melanoma and sarcoid, and is most commonly identified in horses and ponies in their mid to late teens. Equine SCCs arise from cutaneous or mucosal keratinocytes. They initially present as pale coloured plaques that can progress to carcinoma in situ and then to invasive SCC. There is growing evidence that infection of the cutaneous epithelium with a host-specific papillomavirus (EcPV2) has a role in their development. Smegma may play a role in SCC development through its ability to harbour papilloma virus DNA [1].

Clinical signs result from the primary tumour or secondary inflammatory processes. These include purulent or haemorrhagic preputial discharge, preputial swelling, frequent protrusion of the penis, apparent lameness, kicking up at the sheath and assuming a wide-based stance. Owners may notice nonhealing erosions or ulcers on the penis or a more advanced, proliferative, cauliflower-like or solid mass.

Assessment requires visual inspection and palpation of the skin of the penis and prepuce to ascertain number, size, location and mobility. Examination is facilitated by sedation with acepromazine (0.02–0.06 mg/kg i.v.; N.B., priapism risk) and/or detomidine (0.01 mg/kg i.v.). Degree of infiltration and involvement of the corpus cavernosum and corpus spongiosum affects prognosis but this information is difficult to establish. Fine needle aspiration biopsy (FNAB), punch or excisional biopsy are advised, but not always routinely performed. FNAB is a less reliable option since early neoplastic, hyperplastic or dysplastic keratinocytes can all appear similar cytologically. Lymph node metastasis has been reported in 12.5–16.9% of horses with SCC. Lymph node enlargement can sometimes be detected by palpation of the regional lymph nodes; however, false positives and negatives occur. Use of the TNM grading and staging system has been proposed in order to more accurately predict tumour behaviour thus and guide treatment and prognosis [2].

Common treatment options include cryotherapy, topical 5-fluorouracil treatment or surgical intervention. There is limited evidence for piroxicam medication [3]. The surgical technique employed depends on the location and stage of the SCC and options include local excision, segmental posthioplasty (reefing), partial phallectomy, or partial phallectomy with ablation of the sheath and removal of regional lymph nodes (en bloc penile and preputial resection) [4-7]. The choice of surgical technique and details will be discussed. Post-operative histopathological evaluation is indicated since evaluation of surgical margins and the level of differentiation of the SCC will affect the likelihood of metastasis, local recurrence and therefore outcome.

Generalised statements regarding recurrence rates, complication rates and survival times are likely to be misleading due to low numbers in published studies and variations in study design, clinical assessment and surgical methods. Nonsurgical management options are indicated only for ‘precancerous’ or superficial lesions, or following surgical debulking. Local excision and partial phallectomy have a significantly higher recurrence rate than more invasive surgical options. This is due to obtaining incomplete surgical margins or through the progression of remaining early stage lesions. En bloc resections have a lower recurrence rate; however, surgery is more invasive with a higher complication rate. Post-operative survival rates of 64–86% have been reported following en bloc resection techniques [4,5,7,8]. Careful preoperative communication with owners regarding surgical options is vital. Fully informed consent regarding choice of surgical technique, post-operative care, survival rates and complications results in good levels of owner satisfaction following successful en bloc resection procedures and facilitates management of complications when they occur. Recurrence of a SCC is the main factor affecting the prognosis, with the majority of tumours that recur doing so within 1 year (range 14 days–7 years) and an overall reported recurrence rate of 11–28%, regardless of the treatment chosen [2].

[...]