Abstract
Background:
Feline mammary carcinoma (FMC) is a highly aggressive malignancy that shares substantial molecular features with human epidermal growth factor receptor 2 (HER2)-positive and triple-negative breast cancers. Conservative surgical strategies, such as partial mastectomy, typically result in short disease-free interval (DFI), with previous studies reporting postoperative DFIs of 205–428 days. In human traditional Chinese medicine, Trametes robiniophila Murr. (Huaier), containing the bioactive proteoglycan TPG-1, has demonstrated multifaceted antitumor effects, including macrophage activation, inhibition of angiogenesis, suppression of epithelial–mesenchymal transition, and modulation of tumor-associated macrophages. However, to our knowledge, the clinical application of a Huaier-derived proteoglycan preparation (containing TPG-1) in veterinary oncology has not yet been reported.

Case description:
Three spayed female cats (12–14 years old) diagnosed with FMC received partial mastectomy followed by daily oral administration of a Huaier-derived proteoglycan preparation (containing TPG-1; Animmune®, HACHI Co., Ltd., Japan), beginning on postoperative day 2. No additional conventional adjuvant therapies, such as chemotherapy or radiotherapy, were administered. All three cats achieved prolonged DFIs, with no local recurrence or distant metastasis detected through serial thoracic radiography and abdominal ultrasonography. At the time of this report, the DFIs were 612, 695, and 557 days, respectively, exceeding the DFIs typically reported following conservative surgery alone (approximately 205–428 days).

Conclusion:
Despite the presence of high-risk pathological features, including lymphatic invasion, multifocal disease, muscular infiltration, and, in one case, advanced stage III disease with lymph node metastasis, the DFI exceeded previously reported expectations for partial mastectomy alone. These findings suggest that postoperative administration of Huaier-derived proteoglycan (containing TPG-1) may be associated with prolonged DFIs and warrant further clinical investigation in cats with FMC. However, these observations are based on a small uncontrolled case series. No adverse effects were observed during long-term administration in any of the three cats.

Key words: Adjuvant therapy; Feline mammary carcinoma; Huaier-derived proteoglycan; Partial mastectomy; TPG-1.