Diagnosis and Treatment of Tracheal Basal Cell Carcinoma in a Maine Coon and Long-Term Outcome

Introduction

Primary neoplastic and inflammatory tracheal masses are uncommon in cats.^1–8 Previously reported tracheal neoplasms include lymphosarcoma, carcinoma, seromucinous carcinoma, squamous cell carcinoma, adenocarcinoma, and adenoma.^1–6,8 Cats with tracheal and laryngeal neoplasms reportedly present with advanced disease and have poor survival rates; however, isolated cases describing cats living several months following surgical intervention have been published.^1,3,5 There is also one report of a benign inflammatory polyp that was successfully treated in a cat.⁷ Long-term outcomes and prognoses of cats with tracheal masses are not well known, but are generally considered guarded.³

Cats with tracheal masses may present with clinical signs associated with partial airway obstruction, intermittent gagging, and weight loss.^1–8 Historically, treatment recommendations for tracheal masses have depended on both etiology and stage of the tumor. Treatment options include surgical excision, chemotherapy, radiation therapy (RT), or any combination thereof.^2,3 Based on the limited information available, tracheal tumors in cats appear to have a low metastatic rate, which warrants aggressive local therapy.¹ The purpose of this report is to describe the presentation, diagnosis, treatment, and long-term outcome of a Maine coon diagnosed with tracheal basal cell carcinoma (BCC).

Case Report

A 6 yr old castrated male Maine coon presented to its primary veterinarian with a 2 day history of wheezing and tachypnea. At that time, a small amount of clear ocular and nasal discharge was present. The respiratory pattern was stridorous with wheezing. He was treated with azithromycin^a (13.2 mg/kg per os [PO] q 24 hr for 7 days) and lysine^b (5 mL PO q 12 hr for 21 days). The cat returned to the primary veterinarian 1 wk later due to worsening clinical signs. Thoracic radiographs revealed a 2 cm intraluminal tracheal mass at the level of the fourth rib and a diffuse bronchial pattern.

Tracheoscopy performed by the primary veterinarian revealed a white, irregular mass originating from the ventral trachea that nearly occluded the lumen. A brush cytology sample of the mass was obtained. Cytologic diagnosis was moderate neutrophilic inflammation with normal to mildly hyperplastic respiratory epithelium. Given the intrathoracic tracheal mass, respiratory compromise, and worsening clinical condition, the cat was referred to Sage Centers for Veterinary Specialty and Emergency Care.

On presentation, the cat was markedly dyspneic, anxious, and open mouth breathing. He was immediately placed in an oxygen cage with the inspired oxygen set at 40%. He responded to oxygen supplementation, but remained tachypneic. Physical examination revealed pale pink mucus membranes with a capillary refill time of 2 sec. He had significant referred upper airway noise with normal bronchovesicular sounds and no auscultable cardiac abnormalities. He had mild to moderate lameness in all four limbs due to osteoarthritis that developed secondary to a septic polyarthritis of unknown etiology that occurred when he was a kitten.

Complete blood count revealed a mild neutrophilia (14.98×10³/μL; reference range, 2.5–12.5×10³/μL) and monocytosis (1.77×10³/μL; reference range, 0.15–1.7×10³/μL), but was otherwise unremarkable. Hypochloremia (101 mmol/L; reference range, 112–129 mmol/L) was the only abnormality on serum biochemistry.

Due to the marked respiratory distress, resection and anastomosis of the mass was planned. Anesthesia was induced with propofol^c (5 mg/kg IV) and diazepam^d (0.25 mg/kg IV) and maintained with isoflurane^e in 100% oxygen with a mechanical ventilator. Cefazolin^f (22 mg/kg IV) was administered q 90 min during surgery, and fentanyl^g (2 μg/kg/hr) was administered as a continuous rate infusion (CRI). Lactated Ringer's solution^h was administered IV at a rate of 33 mL/hr to adjunct the fentanyl CRI to attain a total fluid volume of 10 mL/kg/hr. Propofol was administered IV to effect during tracheal resection and anastomosis to compensate for the loss of inhalant anesthetic from the surgical site. An 8-French red rubber catheterⁱ was attached to the Y piece of the anesthetic machine and fed through the endotracheal (ET) tube to deliver flow-by oxygen and inhalant anesthetic to the lungs because, initially, the ET tube failed to cross the region of the tracheal resection and anastomosis.

A right lateral intercostal approach to the thorax was performed. A ∼2 cm long annular intraluminal mass was identified in the trachea at the level of the fourth rib. No visible external expansion of the mass was obvious. Blunt dissection was used to isolate the trachea from the surrounding mediastinal tissue. Once isolated, stay sutures were placed using 4-0 polydioxanone^j both caudal and cranial to the mass. The trachea was transected 1 cm cranial to the mass. The 8 French red rubber tube retrofitted for the nonrebreathing circuit was then passed down the lumen of the ET tube to the cut edge of the trachea. The trachea was then transected 1 cm caudal to the mass, and the mass was removed en bloc in conjunction with four tracheal rings. The red rubber tube was advanced across the gap into the caudal trachea to oxygenate the lungs via jet flow. Isoflurane was turned off and IV propofol was administered to maintain a surgical plane of anesthesia. Next, 4-0 polydioxanone was used to preplace sutures approximately 1 mm apart along the dorsal aspect of the trachea, encircling the tracheal rings and ensuring the knots would be external to the lumen. Once all of the preplaced sutures had been placed they were tied, ensuring apposition of the cut edges of the trachea. The ET tube was then advanced beyond the anastomosis site, the cuff was inflated, and isoflurane gas anesthesia was administered. The ventral lumen was closed in a simple interrupted pattern using 4-0 polydioxanone. The anastomotic site was leak-tested by placing saline over the anastomosis and looking for air bubbles. A 10-French thoracostomy drain^k was placed, and the thoracotomy was closed routinely.

Postoperatively, the cat recovered uneventfully in an oxygen cage set at 40% inspired oxygen. He received IV lactated Ringer's solution with fentanyl administered as a CRI at a rate of 3 μg/kg/hr for a total fluid volume of 60 mL/kg/day. A 12 μg/hr fentanyl patch^lwas also placed. Perioperative cefazolin (22 mg/kg IV) was continued q 8 hr for the duration of hospitalization. The thoracotomy site was ice-packed q 6 hr following surgery.

Following recovery, the cat was eupneic. Approximately 16 hr postoperatively he was removed from the oxygen cage, the thoracostomy drain was removed, and the fentanyl CRI was discontinued. He was mildly tachypneic (45 breaths/min); however, the stridor that had been present preoperatively was no longer present, and he had normal bronchovesicular sounds. The cat was discharged 48 hr after presentation. He was prescribed tramadol hydrochloride^m (3 mg/kg PO q 8–12 hr) and meloxicamⁿ (8 drops PO q 24 hr for 3 days) to supplement the fentanyl patch. He also received amoxicillin trihydrate/clavulanate potassium^o (13.75 mg/kg PO q 12 hr). The owners were instructed to strictly confine the cat, monitor his respiration, and return in 2 wk for suture removal and consultation with an oncologist regarding biopsy results and adjunctive treatment.

Histopathologic evaluation revealed a large, nodular, densely cellular, infiltrative mass expanding from the mucosal epithelium, lifting the submucosa, and infiltrating through the cartilage of the tracheal rings. The larger nodules often featured islands of osseous metaplasia. The neoplastic cells were mostly uniform basaloid epithelial cells supported by scant fibrous septa. The cells lacked significant nuclear atypia or pleomorphism, and mitotic figures were rare (<10% of cells/high-power field). The diagnosis of infiltrative BCC with nodular osseous metaplasia was made. The mass was noted to be marginally excised; however, no measured tissue margin was provided. Histologically, there was no overt lymphatic or vascular metastasis within the tumor.

Two weeks postoperatively, the owners returned for consultation with an oncologist. The cat was doing well with neither dyspnea nor tachypnea, and the owners felt he had returned to normal behavior. His incision had healed without complication. Four weeks postoperatively the cat returned for a computed tomography (CT) scan for RT planning.

The CT scan was performed with 3 mm slices extending from the head through the thorax. There was irregular contrast-enhancing skin and subcutaneous tissue at the level of the right fourth and fifth intercostal spaces, which was consistent with scar tissue formation from the recent surgery. There was neither tracheal thickening nor contrast-enhancing tissue surrounding the trachea. There was focal consolidation in the right cranial lung lobe in addition to peribronchial consolidation in the right middle lung lobe. The left lung lobes had an increased interstitial pattern with mediastinal shift to the left consistent with atelectasis. The cardiac silhouette was markedly enlarged with myocardial thickening of the left ventricle and left atrial enlargement. Pulmonary changes were consistent with atelectasis, and it was recommended that thoracic radiographs be taken when the cat was awake to rule out metastatic disease. Cardiac changes were consistent with hypertrophic cardiomyopathy, and an echocardiogram was recommended prior to further RT planning.

An echocardiogram performed 4 days later by a board-certified radiologist revealed no significant cardiac lesions. Three-view thoracic radiographs taken the same day revealed no tracheal or pulmonary lesions.

Based on CT reconstruction, a three-dimensional computerized treatment plan was formulated using a Varian Eclipse Treatment Planning System^p. The clinical target volume (CTV) was determined using the intratracheal surgical scar with an additional 1.0 cm margin. The planning target volume (PTV) was determined using an additional 1.0 cm margin beyond the CTV. The prescribed dose was 19 fractions of 250 centigray (cGy) for a total dose of 4,750 cGy. This dose was prescribed to the 95% isodose line. The field size in right lateral was 6.4 cm × 6.0 cm. Approximately 6.4 cm of the thoracic portion of the trachea (i.e., from the thoracic inlet to the carina) was irradiated. No portion of the extrathoracic trachea was irradiated. Radiation was administered with a Varian 2100C linear accelerator^q using 6 MV photons. Radiation was delivered using bilateral parallel opposed fields with the isocenter placed at the center of the PTV (Figure 1). No wedges, blocks, or other beam-modifying devices were used. For each treatment, anesthesia was induced in a chamber with isoflurane, and the patient was then intubated and maintained on isoflurane and 100% oxygen. There were no anesthetic complications associated with any of the radiation treatments.

View Figure

• Download as Powerpoint
• Download Figure

The thoracic spinal cord, heart, and lungs were the dose-limiting structures within the radiation field. The thoracic spine received a mean dose of 2,005 cGy and a maximum dose of 4,980 cGy. The heart received a mean dose of 390 cGy and a maximum dose of 3,950 cGy. The lungs received a mean dose of 915 cGy and a maximum dose of 5,225 cGy (Figure 2).

View Figure

• Download as Powerpoint
• Download Figure

On the fifth day of treatment, the radiation site was warm to the touch. Aloe vera spray^r was prescribed for topical use q 8 hr. Thoracic radiographs taken prior to the ninth dose were unchanged compared with those taken prior to initiation of RT. Mild, dry, desquamation was also noted at that time. On day 12, prednisolone^s (1.3 mg/kg PO q 24 hr for 14 days) was prescribed due to frequent swallowing, suggestive of radiation-induced esophagitis. The excessive swallowing resolved within 24 hr of initiation of prednisolone. The skin in the radiation field remained free of significant irritation throughout the course of treatment, and the cat remained eupneic.

The cat was re-evaluated 1 wk following conclusion of the full course of RT. Thoracic auscultation revealed normal bronchovesicular sounds without referred upper airway noise and no wheezing or stridor. Two-view thoracic radiographs revealed no pulmonary nodules, lymphadenopathy, or lung pathology. The tracheal lumen appeared mildly narrowed in the midthorax (by 1 mm) and had mild dilation distally. The prednisolone was decreased to 0.65 mg/kg PO q 24 hr for 3 wk, and the owners were asked to come back at that time to reevaluate the cat.

As planned, the cat presented 4 wk after completing the RT for reevaluation and thoracic radiographs. He remained eupneic with no clinical signs of respiratory compromise. Thoracic auscultation was unremarkable. Three-view thoracic radiographs showed neither pulmonary nodules nor lymphadenopathy; however, a mild cardiomegaly was present. No radiographic changes consistent with radiation-induced pneumonitis were present. The prednisolone dose was decreased from 0.65 mg/kg PO q 24 hr to 0.65 mg/kg PO q 48 hr for 1 wk and was then discontinued. The owners were advised to let the cat return to normal activity and to return in 2–3 mo for reevaluation, including thoracic radiographs and possibly a thoracic CT. The owners did not return to have their cat evaluated as planned.

At the time this report was written, 32 mo after initial presentation, the owners were contacted by telephone. The owners reported that the cat was doing well at home and had not experienced any respiratory difficulty since treatment.

Discussion

Tracheal tumors in cats are uncommon, and little is known regarding long-term outcomes and prognoses. The reported age range of cats diagnosed with tracheal tumors is 2–13 yr of age; however, though the majority of reported cases are 9–13 yr.^1–4,7,8 Previous reports indicate either an equal distribution between the sexes or an increased incidence in male cats; however, a more recent publication found that spayed female cats were more commonly afflicted.^1–4 Domestic shorthair and Siamese cats are the most commonly affected breeds; however, domestic longhair, Himalayans, and Persians are also reported to have tracheal tumors.^1–4,7,8 To the authors’ knowledge, this is the first reported case of a Maine coon with a tracheal mass.

The cat in this study had an acute onset of wheezing, tachypnea, and stridorous respiration that was progressive in nature. These findings were consistent with previous reports of cats with tracheal tumors.^1–8 In the patient reported herein, a possible explanation for the rapid decompensation seen between brush cytology acquisition by the primary veterinarian and referral may have been secondary to swelling and edema from the cytology procedure, leading to increased luminal obstruction.

In stable patients, radiography is reportedly the diagnostic procedure of choice to identify tracheal tumors, particularly as they are outlined by air and usually appear as a solitary, distinct mass.^2,3 A recent study evaluating cats with laryngeal and tracheal masses identified radiographic abnormalities in 88% of cats, demonstrating both soft-tissue opacities and tracheal stenosis.¹ The same study found the presence of a soft-tissue opacity on radiographic examination to be a significant indicator of neoplasia in cats with laryngeal and tracheal masses.¹ Overexpansion of the lungs together with flattening of the diaphragm and prominent pulmonary vasculature have also been described.^3,4

Bronchoscopy may also be diagnostically useful because it permits direct visualization of the mass as well as the acquisition of brush cytologies and/or biopsies.³ The study by Jakubiak et al. (2005) describes five cats with either laryngeal or tracheal masses that were initially diagnosed with lymphoid hyperplasia based on either cytologic or histopathologic samples that were subsequently diagnosed as neoplasms.¹ Given that finding, those researchers recommended performing a second biopsy in cats initially diagnosed with lymphoid hyperplasia. It is possible that inflammation masks the underlying neoplasia in those cats. Needle aspirations of BCC have been described, which have found the cytologic features to be nonspecific, likely resulting in underdiagnosis of the tumor.⁹ The brush cytology in this case did not correlate with the resulting histopathology of the mass.

BCCs normally occur on the skin, arising from the pluripotent basal epithelial cells that give rise to the epidermis and adnexa. They are the most common type of skin tumor in the cat, accounting for 15–26% of feline skin tumors, and they are almost always benign.^9,10 Cutaneous BCCs typically have a high mitotic rate despite typically being benign tumors; however, in this case, the mitotic rate was very low.⁹ It is interesting to note that most BCCs of the skin remain firmly fixed to the overlying skin, but do not typically invade the underlying fascia.⁹ The tracheal BCC in this study infiltrated the nearby cartilaginous tissue.

Given that the mass had only been marginally excised and there was cartilaginous invasion, irradiation of the site was indicated to optimize the possibility of a long-term disease-free interval.¹⁰ Chemotherapy has been described in the treatment of metastatic BCC in conjunction with surgical excision and RT.¹⁰ Given the localized nature of the disease and the lack of vascular or lymphatic invasion in this patient, chemotherapy was not recommended.

The thoracic spine, heart, and lungs were all included in the radiation field. All are susceptible to late radiation toxicities because of their slowly proliferative nature.¹¹ Late effects are the dose-limiting complications of RT and must be considered when developing any RT plan.¹² The cat in this study suffered no clinically apparent late effect toxicities in the 32 mo follow-up period (according to the owner); however, the cat was not reevaluated by a veterinarian beyond 1 mo following the RT.

Mild, acute effects noted during RT included esophagitis and desquamation, which were due to the rapidly proliferative nature of those tissues.¹¹ The presumed esophagitis was treated with prednisolone, and the desquamation was managed with aloe vera. Both conditions resolved quickly. This rapid resolution was expected because early effects tend to be self-limiting with a rapid recovery.¹¹

The authors acknowledge that tracheal resection and anastomosis alone may have provided adequate local control with a comparable outcome to RT in addition to surgery in this case. Clinical judgment dictated that adjunctive RT should be performed, considering the invasive nature of the mass despite the low mitotic index and narrow surgical margins. The decision to use RT in the adjuvant setting should be based on surgical margins and clinical impression because surgery alone may be sufficient to provide a long-term disease-free interval in some cases.

One limitation of this case report is the absence of direct clinical reevaluation of the cat beyond 1 mo after completing RT to verify either the presence or absence of local disease progression or distant metastasis. There is value in knowing the cat was alive and apparently healthy without overt evidence of clinical manifestations of disease 32 mo following diagnosis and treatment of tracheal BCC; however, concrete conclusions regarding disease progression following treatment in this case cannot be made.

Conclusion

This case report describes the first documented intratracheal BCC in a cat. Both surgical excision and RT were implemented in the treatment of this tumor, which resulted in complete resolution of clinical signs for >32 mo. This case is an indication that prolonged resolution of clinical signs can be achieved with BCC of the feline thoracic trachea with adequate local therapy and minimal side effects.