Ovarian Neoplasia

Ovarian neoplasia encompasses a diverse group of primary and metastatic tumors arising from the ovarian stroma, epithelium, or germ cells. In veterinary medicine, these tumors are relatively uncommon but clinically significant due to their potential for hormonal imbalances, abdominal mass effects, and malignant dissemination. The ovaries are paired, ovoid organs located caudal to the kidneys within the ovarian bursa, attached to the dorsal abdominal wall by the mesovarium. They serve dual roles: gamete production and endocrine secretion of estrogens, progesterone, and androgens. Ovarian tumors can be classified based on their cell of origin: epithelial tumors (papillary adenoma, adenocarcinoma), germ cell tumors (dysgerminoma, teratoma), and sex cord-stromal tumors (granulosa cell tumor, thecoma, luteoma, Sertoli cell tumor). Surgical management, typically ovariohysterectomy (OHE) or ovariectomy (OVE), is the cornerstone of treatment, with the extent of surgery and adjunctive therapy dictated by tumor type, stage, and patient status.

The exact etiology of ovarian neoplasia in dogs and cats remains largely unknown, but several factors are implicated. Genetic predisposition is suggested by breed-specific incidences, such as granulosa cell tumors being more common in certain breeds. Hormonal influences are significant; ovarian tumors often occur in intact, middle-aged to older females, and prolonged estrogen stimulation may promote tumorigenesis. Chronic inflammation or irritation of the ovarian epithelium, analogous to human ovarian cancer, may contribute to epithelial tumor development. Environmental factors, including exposure to carcinogens or ionizing radiation, are theoretical but unproven. In cats, ovarian neoplasia is rare, but when present, it is often malignant, suggesting a possible viral or genetic etiology. Additionally, developmental abnormalities, such as ovarian remnant syndrome, can lead to neoplastic transformation of residual ovarian tissue. The molecular mechanisms involve dysregulation of cell cycle control, apoptosis, and angiogenesis, with specific oncogenes and tumor suppressor genes implicated in human ovarian cancer, though analogous pathways in veterinary species are less defined.

Ovarian neoplasia is uncommon in dogs and cats, accounting for approximately 0.5-1.2% of all canine tumors and less than 1% of feline tumors. The mean age of affected dogs is 10-12 years, with a range of 1-20 years. Certain breeds appear predisposed: granulosa cell tumors are reported more frequently in German Shepherds, Boxers, and Yorkshire Terriers; dysgerminomas in Boxers and Collies; and teratomas in young dogs, often under 2 years. Cats are typically older (mean 10-12 years) and have a higher proportion of malignant tumors, particularly adenocarcinomas. Sex is inherently female, but intact females are at risk; early ovariohysterectomy virtually eliminates the risk. No significant geographic or environmental predispositions are documented. In working dogs, there is no increased incidence, but reproductive status is a key factor. The incidence of ovarian tumors in dogs is lower than that of mammary tumors, but they are more common than testicular tumors in males.

Ovarian tumors arise from the three main cell types of the ovary: surface epithelium, germ cells, and sex cord stroma. Epithelial tumors, including adenomas and adenocarcinomas, originate from the ovarian surface epithelium (mesothelium) and can be cystic or solid. They may invade the ovarian stroma and metastasize via peritoneal seeding, lymphatic, or hematogenous routes. Germ cell tumors, such as dysgerminomas and teratomas, arise from primordial germ cells. Dysgerminomas are malignant, often bilateral, and metastasize to regional lymph nodes and lungs. Teratomas contain tissues from multiple germ layers and are usually benign, but malignant transformation can occur. Sex cord-stromal tumors, including granulosa cell tumors, thecomas, and luteomas, arise from the ovarian stroma and granulosa cells. Granulosa cell tumors are the most common ovarian tumor in dogs and are often functional, secreting estrogen or progesterone, leading to clinical signs such as cystic endometrial hyperplasia, pyometra, or alopecia. They can be benign or malignant, with malignancy characterized by capsular invasion and metastasis. The pathophysiology of hormonal secretion leads to systemic effects, including bone marrow suppression (estrogen-induced), which can cause pancytopenia and secondary infections. Tumor growth can cause abdominal distension, pain, and gastrointestinal signs due to mass effect. Malignant tumors may spread to the omentum, liver, and lungs, resulting in effusions and respiratory signs.

Intrinsic factors include age (middle-aged to older), breed (as noted), and intact reproductive status. Genetic mutations and familial predisposition are suspected but not fully characterized. Hormonal imbalances, such as prolonged estrogen exposure, may promote tumor development. Extrinsic factors are less defined but may include environmental carcinogens, obesity, and dietary factors. Prior ovarian remnant syndrome or incomplete ovariohysterectomy can predispose to neoplastic transformation of residual tissue. In cats, the risk is higher in intact females, and certain breeds like Siamese may be overrepresented. There is no evidence that parity or number of estrous cycles affects risk. Management practices, such as the use of hormonal contraceptives, have not been conclusively linked to ovarian neoplasia in veterinary species.

Clinical signs of ovarian neoplasia are often insidious and may be absent in early stages. Common presentations include abdominal distension, palpable abdominal mass, lethargy, anorexia, weight loss, and vomiting. Hormonally active tumors, particularly granulosa cell tumors, can cause signs related to hyperestrogenism or hyperprogesteronism. In dogs, hyperestrogenism may manifest as persistent estrus, vulvar swelling, serosanguineous vaginal discharge, cystic endometrial hyperplasia, pyometra, and alopecia. Estrogen-induced bone marrow suppression can lead to anemia, leukopenia, and thrombocytopenia, resulting in pale mucous membranes, fever, and bleeding tendencies. Hyperprogesteronism can cause mammary gland enlargement, galactorrhea, and immunosuppression. In cats, clinical signs are often vague, with weight loss and abdominal mass being common. Malignant tumors may cause ascites, pleural effusion, and respiratory distress due to metastasis. On palpation, an ovarian mass may be detected as a firm, nodular structure in the mid-abdomen, but it can be difficult to differentiate from other abdominal masses. Rectal examination may reveal a mass in the ovarian region. Systemic signs of paraneoplastic syndromes, such as fever, polyarthritis, or hypertrophic osteopathy, are rare but possible.

Differential diagnoses for ovarian neoplasia include: 1) Pyometra or cystic endometrial hyperplasia (CEH) – these conditions present with vaginal discharge, polyuria/polydipsia, and systemic illness; imaging shows uterine enlargement, not ovarian mass. 2) Ovarian remnant syndrome – residual ovarian tissue after OHE can cause estrus-like signs and cystic structures on ultrasound, but no distinct mass. 3) Mammary gland neoplasia – masses in the caudal mammary glands may be mistaken for ovarian masses on palpation, but they are superficial and associated with the mammary chain. 4) Splenic or hepatic masses – these can present as abdominal masses but are located in specific organ regions; ultrasound and cytology differentiate. 5) Gastrointestinal foreign body or intussusception – these cause acute vomiting and abdominal pain, with imaging showing intestinal obstruction. 6) Uterine leiomyoma or leiomyosarcoma – these are uterine masses that may be palpable and cause similar signs; ultrasound and histopathology are definitive. 7) Abdominal lymphadenopathy – enlarged lymph nodes due to lymphoma or metastasis can mimic ovarian masses; cytology is diagnostic. 8) Peritonitis or abscess – these cause fever, pain, and leukocytosis; imaging shows fluid or localized infection. 9) Adrenal gland tumors – these can cause hormonal signs and abdominal masses, but are located craniomedial to the kidneys; ultrasound and endocrine testing differentiate. 10) Renal tumors – these are located in the retroperitoneal space and may cause hematuria; ultrasound and excretory urography are helpful.

The diagnostic approach to suspected ovarian neoplasia begins with a thorough history and physical examination, including careful abdominal palpation. If an ovarian mass is suspected, the following steps are recommended: 1) Baseline bloodwork (CBC, serum biochemistry, urinalysis) to assess overall health and detect paraneoplastic effects such as anemia or leukocytosis. 2) Abdominal radiography to identify a soft tissue mass in the mid-abdomen, assess for mineralization (teratomas), and evaluate for metastasis (e.g., lung patterns on thoracic radiographs). 3) Abdominal ultrasonography is the imaging modality of choice to confirm the ovarian origin of the mass, characterize its internal structure (cystic, solid, mixed), and evaluate the contralateral ovary, uterus, and abdominal organs for metastasis. Ultrasound-guided fine-needle aspiration (FNA) of the mass can provide cytological evidence of neoplasia, though it may not differentiate tumor types definitively. 4) If FNA is inconclusive or malignancy is suspected, advanced imaging such as computed tomography (CT) or magnetic resonance imaging (MRI) may be used to better define the mass, assess vascular invasion, and plan surgery. 5) Preoperative staging includes thoracic radiographs (three views) to rule out pulmonary metastasis and abdominal ultrasound to detect hepatic, splenic, or lymph node involvement. 6) Definitive diagnosis requires histopathological examination of the excised tumor. Intraoperative assessment includes inspection of the abdominal cavity for carcinomatosis, biopsy of suspicious lesions, and collection of peritoneal fluid for cytology if present. 7) In cases where surgery is not immediately performed, ultrasound-guided biopsy may be considered, but this carries a risk of tumor seeding and is generally avoided if surgical excision is planned.

Complete blood count (CBC) may reveal anemia, leukocytosis, or thrombocytopenia, particularly in cases of estrogen-secreting tumors causing bone marrow suppression. Serum biochemistry may show elevated liver enzymes (ALP, ALT) if metastasis is present, or hypercalcemia in some malignancies. Urinalysis may be normal or show hematuria if there is uterine involvement. Coagulation panel (PT, aPTT, platelet count) is recommended to assess surgical risk, especially if there is evidence of bleeding or thrombocytopenia. Blood gas analysis may be indicated in severely debilitated patients. Inflammatory biomarkers such as C-reactive protein (CRP) may be elevated in malignant tumors. Hormonal assays (estradiol, progesterone, testosterone) can be helpful in diagnosing functional tumors, but are not routinely performed. Peritoneal fluid analysis, if ascites is present, may show neoplastic cells or evidence of inflammation. Cytology of FNA samples from the ovarian mass can reveal epithelial, germ cell, or stromal cell characteristics, but histopathology is required for definitive diagnosis.

Radiography: On abdominal radiographs, ovarian tumors appear as soft tissue masses in the mid-abdomen, often caudal to the kidneys. They may be round or lobulated, and mineralization can be seen in teratomas. Thoracic radiographs are essential for staging, as pulmonary metastasis appears as nodular interstitial patterns. Ultrasonography: This is the most valuable imaging modality. Ovarian tumors appear as complex masses with cystic and solid components. Granulosa cell tumors often have a characteristic 'honeycomb' appearance due to multiple cysts. The contralateral ovary should be evaluated for bilateral involvement. Ultrasound also allows assessment of the uterus for concurrent pathology (e.g., CEH, pyometra) and detection of abdominal metastasis. Color Doppler can assess vascularity. CT: Provides detailed cross-sectional images, useful for surgical planning, especially in large or invasive tumors. It can detect lymph node enlargement, peritoneal carcinomatosis, and liver metastasis. MRI: Offers superior soft tissue contrast and is useful for characterizing the tumor and its relationship to surrounding structures, but is less commonly used due to cost and availability. Excretory urography or CT urography may be used to rule out ureteral obstruction if the mass is large. Fluoroscopy is rarely used but can guide biopsy procedures.

Cytology: Fine-needle aspiration of ovarian masses can yield cells that are suggestive of the tumor type. Epithelial tumors may show clusters of cuboidal to columnar cells with anisocytosis and anisokaryosis. Granulosa cell tumors often have cells with abundant cytoplasm and characteristic Call-Exner bodies (small fluid-filled spaces). Dysgerminomas have large, round cells with prominent nucleoli. Teratomas may contain squamous cells, sebaceous cells, or other differentiated tissues. However, cytology is often non-diagnostic due to the cystic nature of many tumors. Histopathology: The excised tumor should be submitted for histopathological examination. Grossly, ovarian tumors can be solid, cystic, or mixed. Microscopically, the tumor type is determined based on cell morphology and architecture. Granulosa cell tumors have cells arranged in cords, nests, or follicles, with occasional Call-Exner bodies. Thecomas consist of spindle cells with lipid vacuoles. Luteomas have large, polyhedral cells with abundant eosinophilic cytoplasm. Dysgerminomas are composed of large, round cells with vesicular nuclei and a high mitotic index. Teratomas contain tissues from at least two germ layers, such as skin, hair, bone, or neural tissue. Malignancy is determined by capsular invasion, vascular invasion, and metastasis. Immunohistochemistry (IHC) can be used to differentiate tumor types: inhibin and calretinin are positive in sex cord-stromal tumors, while cytokeratin is positive in epithelial tumors. Surgical margins should be evaluated for completeness of excision.

The primary treatment for ovarian neoplasia is surgical excision, typically via ovariohysterectomy (OHE) or ovariectomy (OVE). OHE is preferred because it removes the entire reproductive tract, eliminating the risk of future uterine pathology and ensuring complete removal of ovarian tissue. The surgical approach is a ventral midline celiotomy. The patient is positioned in dorsal recumbency, and the abdomen is clipped and aseptically prepared. A midline incision is made from the umbilicus to the pubis, extending cranially as needed for large masses. The ovarian pedicles are identified and ligated. For a large tumor, the pedicle may be thickened and vascular; careful dissection and ligation with absorbable suture (e.g., polydioxanone, polyglactin 910) or an electrosurgical vessel-sealing device (e.g., LigaSure) is recommended. The suspensory ligament may need to be transected to mobilize the ovary. The uterine body is ligated just cranial to the cervix and transected. The abdomen is closed routinely. In cases of malignant tumors with metastasis, debulking surgery may be performed to remove visible tumor masses, but complete excision may not be possible. Adjunctive therapy: Chemotherapy may be considered for malignant tumors, particularly dysgerminomas and adenocarcinomas. Protocols using carboplatin or cisplatin have been described, but data are limited. Radiation therapy is rarely used due to the difficulty of targeting the abdomen. Hormonal therapy is not effective. Postoperative care includes pain management with opioids (e.g., hydromorphone 0.05-0.1 mg/kg IV q4-6h) and NSAIDs (e.g., carprofen 2.2 mg/kg PO q12h) if renal function is normal. Antibiotics are not routinely indicated unless there is contamination. The patient should be monitored for signs of hemorrhage, infection, and anesthetic recovery.

The prognosis for ovarian neoplasia depends on tumor type, stage, and completeness of excision. Benign tumors, such as adenomas and benign teratomas, carry an excellent prognosis after complete surgical excision. Granulosa cell tumors have a good prognosis if completely excised, with a reported 5-year survival rate of over 80% in dogs. However, malignant granulosa cell tumors with metastasis have a guarded prognosis. Dysgerminomas are malignant and have a moderate to poor prognosis, with a high rate of metastasis. Epithelial adenocarcinomas are also malignant and carry a poor prognosis, especially if there is peritoneal dissemination. Cats with ovarian adenocarcinoma have a very poor prognosis due to early metastasis. Negative prognostic indicators include tumor rupture, capsular invasion, vascular invasion, metastasis at the time of surgery, and high histologic grade. The overall recurrence rate after OHE for benign tumors is low. For malignant tumors, the median survival time may be several months to a year with adjunctive chemotherapy. The prognosis is also influenced by the patient's overall health and the presence of paraneoplastic syndromes, such as bone marrow suppression, which can complicate recovery.

Postoperative follow-up is essential to monitor for recurrence and metastasis. The patient should be re-examined at 10-14 days for suture removal and assessment of wound healing. Abdominal ultrasonography should be repeated at 1, 3, 6, and 12 months postoperatively to evaluate for local recurrence or metastasis, especially in cases of malignant tumors. Thoracic radiographs should be taken at 3, 6, and 12 months to screen for pulmonary metastasis. For patients with functional tumors, serial hormone levels (e.g., estradiol, progesterone) can be monitored to detect recurrence. The patient's activity should be restricted for 2 weeks postoperatively to allow healing. Long-term monitoring includes regular physical examinations and owner education on signs of recurrence, such as abdominal distension, weight loss, or changes in appetite. For patients with bone marrow suppression, serial CBCs are recommended until values normalize. The prognosis and follow-up plan should be discussed with the owner, emphasizing the importance of early detection of recurrence.

Pearls: 1) Always perform a thorough abdominal exploration during OHE for ovarian tumors, including inspection of the liver, spleen, omentum, and lymph nodes for metastasis. 2) In cases of large ovarian tumors, ligate the ovarian pedicle carefully, as it may be highly vascular; use a triple ligation technique or a vessel-sealing device to ensure hemostasis. 3) If the tumor is cystic, aspirate the fluid before exteriorization to reduce the risk of rupture and spillage. 4) Consider performing an ovariohysterectomy rather than ovariectomy to prevent future uterine disease and ensure complete removal of ovarian tissue. 5) Submit the entire tumor for histopathology, and if malignancy is suspected, consider staging with abdominal ultrasound and thoracic radiographs preoperatively. 6) In cats, ovarian tumors are often malignant, so be aggressive in surgical excision and staging. Pitfalls: 1) Failure to identify the ovarian remnant if a previous OHE was performed; always check for residual ovarian tissue in the sublumbar region. 2) Rupturing the tumor during surgery, which can lead to peritoneal seeding and recurrence. 3) Overlooking a contralateral ovarian tumor; always inspect both ovaries. 4) Inadequate ligation of the ovarian pedicle, leading to life-threatening hemorrhage. 5) Not performing preoperative staging, resulting in incomplete excision of metastatic disease. 6) Ignoring paraneoplastic syndromes, such as bone marrow suppression, which can increase surgical risk; stabilize the patient before surgery if possible.

Perioperative antimicrobial prophylaxis: Cefazolin 22 mg/kg IV at induction, repeated every 90 minutes during surgery. Postoperative antibiotics are not routinely needed unless contamination occurred. Analgesia: Preoperative: Opioid (e.g., hydromorphone 0.05-0.1 mg/kg IV or morphine 0.5-1 mg/kg IM) or a pure mu agonist. Intraoperative: Consider a constant rate infusion (CRI) of fentanyl (5-10 mcg/kg/hr IV) or lidocaine (25-50 mcg/kg/min IV) for multimodal analgesia. Postoperative: NSAIDs (e.g., carprofen 2.2 mg/kg PO q12h for 3-5 days, or meloxicam 0.1 mg/kg PO q24h) if renal function is normal. Opioids may be continued for 24-48 hours as needed. Local anesthesia: Incisional line block with bupivacaine (1-2 mg/kg) or a splash block. For patients with estrogen-induced bone marrow suppression, supportive care includes broad-spectrum antibiotics (e.g., amoxicillin-clavulanate 13.75 mg/kg PO q12h) and, if severe, blood transfusion. Chemotherapy protocols for malignant tumors: Carboplatin 300 mg/m² IV every 3 weeks for 4-6 cycles, or doxorubicin 30 mg/m² IV every 3 weeks. These should be administered by a veterinary oncologist. Antiemetics (e.g., maropitant 1 mg/kg SC q24h) may be used if chemotherapy is given. Chondroprotectants are not relevant. Always adjust dosages in patients with renal or hepatic impairment.

The veterinary literature on ovarian neoplasia is limited to retrospective case series and case reports. A landmark study by Patnaik et al. (1976) described the clinical and pathologic features of ovarian tumors in dogs, establishing the classification system used today. More recent studies, such as that by Sforna et al. (2003), reported on the surgical outcomes of granulosa cell tumors in dogs, with a good prognosis after OHE. A study by Klein (2001) evaluated the use of chemotherapy in canine ovarian adenocarcinomas, showing a modest response to platinum-based agents. In cats, a retrospective study by Miller et al. (2013) found that ovarian tumors are rare but highly malignant, with a poor prognosis. Consensus guidelines from the ACVS and ECVS recommend OHE as the treatment of choice for ovarian neoplasia, with staging and adjunctive chemotherapy for malignant tumors. There are no prospective randomized trials due to the rarity of the disease. The evidence supports early surgical intervention and complete excision for the best outcomes. Future research should focus on molecular markers and targeted therapies.