History and Initial Treatment

Pixelle, a 13 year old Shih Tzu, started her long cancer journey in June of 2020 when she was diagnosed with a left-sided adrenal mass after undergoing a thorough workup for vomiting, polyuria/polydipsia, and intermittent urinary incontinence. A pheochromocytoma was ruled out as a low-dose dexamethasone suppression test was consistent with Cushing’s Disease (cortisol secreting tumor). 

Surgery was performed to remove the adrenal mass in July 2020. Excision of the mass was marginal, and invasion of the surrounding fat through the capsule was noted. Histopathology reported an adrenocortical carcinoma. Pixelle was treated with a five-dose course of intravenous Carboplatin from August to November of 2020. Restaging in December 2021 revealed a very slowly increasing right adrenal nodule, hyperechoic hepatomegaly, and a nodule adjacent to the left renal vein. 

In March 2022, local recurrence and a right adrenal nodule invading the caudal vena cava were noted. Pixelle was started on Palladia. In June 2022, local progression and a liver mass were seen on abdominal ultrasound. The liver mass was resected surgically. Initially presumed to be a primary liver carcinoma, histology revealed that it was a metastatic adrenocortical carcinoma. Subsequently, Pixelle was treated with several chemotherapy drugs following her surgical recovery, including 5-FU, Doxorubicin, Gemcitabine, and Carboplatin+Gemcitabine. The progressive disease/recurrence of the local tumor and main liver metastasis did not respond to traditional chemotherapy.

An abdominal ultrasound in March 2023 included the following findings:

• Severely progressive liver mass – documented adrenal carcinoma metastasis
• Progression of the nodule into the gallbladder (malignant in appearance)
• Mild progression of local metastasis of the left adrenal gland anteriorly resected; invasion of the vena cava strongly suspected
• Stable right adrenal nodule with slight invasion of the vena cava

Pixelle’s oncologist contacted FidoCure in March 2023 to enroll her for DNA sequencing of the original adrenal mass. 

Before + After Olaparib X-Rays 

Before + After Olaparib X-Rays 

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Precision Medicine Results and Treatment

Pixelle’s FidoCure Precision Medicine DNA sequencing revealed two mutations indicating potential therapeutic approaches, BRCA1 and PTEN; and three mutations of unknown clinical significance, ARID1A, P53, and TSC1. 

Gene: BRCA1  Mutation: Copy Number Loss

Therapy Considerations: Olaparib - 3 mg/kg/day PO; platinum-based chemotherapy

BRCA1 (Breast Cancer Susceptibility Gene 1) is a well-described tumor suppressor gene, particularly in human breast cancer. Normal BRCA proteins function in DNA repair and chromosome stability. BRCA1 regulates the key effectors that control the G2/M checkpoint, and is therefore believed to be involved in regulating the onset of mitosis. BRCA1 has other functions besides DNA damage sensing and cell cycling regulation, such as E3 ubiquitin ligase activity, chromatin remodeling, and homologous recombination. A common function between BRCA1 and BRCA2, homologous recombination is an essential DNA repair system that enables the error-free recovery of double strand breaks. Double strand breaks are the most severe DNA damage, the accumulation of which results in genetic translocation and cell death (Hatano et al., 2020).

BRCA1 and BRCA2 copy number loss due to their impact on gene expression and protein structure can contribute to disease development (Krepischi et al., 2012). Copy number variations (CNVs) can be classified as somatic or germline. Germline CNVs represent 4 to 28% of all inherited BRCA mutations depending on the study (Kwong et al., 2015). Pathogenic CNVs are more frequent in BRCA1 than BRCA2 and reach 27% and 8% of BRCA genetic variations respectively (Boujemaa et al., 2021).

In canine mammary tumors, losses in chromosome regions of BRCA1 and BRCA2 genes were found in 18 (16.9%) and 3 (2.7%) of cases respectively, in a study evaluating 117 tumors from 69 dogs (Borge et al., 2015). Platinum-based agents may be of increased benefit in BRCA1/2 mutant tumors and loss and often improve survival of human patients (Mylavarapu et al., 2018). Although BRCA-mutated cancer generally exhibits high-grade histology and aggressive phenotypes, it can respond favorably to platinum-containing chemotherapy. This platinum sensitivity is most likely due to BRCA-associated homologous recombination deficiency that fails to recover platinum-induced interstrand crosslinks (Deans; West, 2011).

Gene: PTEN  Mutation: Copy Number Loss

Therapy Considerations: Rapamycin (Sirolimus) - 0.1 mg/kg/day PO

PTEN or phosphatase and tensin homolog is a tumor suppressor frequently altered in numerous human cancers. Alterations in PTEN have also been identified in canine malignancies. The normal function of PTEN is negative regulation of the AKT/PI3K/mTOR controlling a plethora of cellular processes, including survival, proliferation, energy metabolism and cellular architecture (Song et al., 2012; Cantley, 2002). Impairment of PTEN function through multiple mechanisms, including through non-synonymous mutations, results in PIP3 accumulation and constitutive activation of catabolic downstream AKT/mTOR signaling.

Loss of PTEN activity leads to genomic instability and provides a setting for the accumulation of other deleterious mutations. PTEN is frequently mutated in many types of human cancer (Sansal, Sellers, 2004). PTEN copy number loss (<2 copies) was identified in 20% of non-small cell lung cancer and was associated with shorter progression-free survival (HR 2.54, P<0.001), shorter overall survival (HR 4.04, P<0.001) and lower likelihood to respond to EGFR inhibitors in a human study (Fidler et al., 2011). In relapsed prostatic cancer, human patients whose tumors had copy number loss of PTEN and copy number gain of c-MYC had significantly increased genetic instability compared to tumors with normal PTEN and c-MYC status (p < 0.0001). These patients were determined to have a worse prognosis (HR 3.21, p = 0.0004)(Zafarana et al., 2012). Copy number loss of PTEN provides a rationale for the use of molecular-targeted agents, such as MYC, PI3K-PTEN-AKT, and/or PARP inhibitors (Zafarana et al., 2012).

In humans, rapamycin has been used to treat brain, breast, kidney and pancreatic tumors. In dogs, rapamycin has been explored in canine osteosarcoma, mast cell tumor, mammary carcinoma and melanoma.

Pixelle began treatment with the targeted therapy, Olaparib, a small molecule PARP enzyme inhibitor that can be indicated by BRCA1 or BRCA2 alterations on May 2, 2023. She began treatment at the recommended starting dose of 3 mg/kg once daily PO, and escalated to the no-observable-adverse-effect level (NOAEL) of 5 mg/kg once daily PO on June 10, 2023. She did not experience any adverse effects at the initial or escalated dosing levels. Concomitant medications were: Telmisartan, Amlodipine, Clopidogrel, Ursodiol, Fortiflora.

Pixelle returned to her oncologist’s office on July 14, 2023 for restaging. On abdominal ultrasound, both the local recurrence and the main liver metastasis were significantly improved. The liver mass, previously 6.6 X 8.6cm, was 3.4cm in diameter, with the margins still well defined. The left adrenal gland, previously 12.6 X 23mm, was bilobed with the most caudal pole 12.6mm in diameter. The right adrenal gland was unchanged in size.

Most recently, Pixelle visited her oncologist on Dec. 8, 2023 for restaging including an abdominal ultrasound. She was reportedly doing well clinically, still with no adverse effects related to the Olaparib. The hepatic metastasis had continued to decrease in size (down to 2.4cm in diameter). The left adrenal mass (recurrence of previously-resected adrenocortical carcinoma) was stable in size. An associated thrombus in the caudal vena cava had, unfortunately, progressed significantly in size (neoplastic invasion vs pure thrombus). Due to the findings involving the thrombus vs neoplastic invasion, Rapamycin (Sirolimus) 0.12mg/kg EOD (escalating to q24 if well tolerated); and Rivaroxaban (Xarelto) were added.

We want to thank Dr. Cyril Parachini-Winter, m.v., MS, Dipl. ACVIM (oncology), Vétérinaire Oncologue and the team at Centre DMVet in Blainville, Quebec, Canada for sharing Pixelle’s story. FidoCure continues to follow her cancer journey and wishes her well.