Globo H於犬惡性乳腺腫瘤之預後價值的評估與探討

Abstract

Globo H為一常見分布於癌細胞表面的醣類抗原，它在正常細胞的表現受限，因此可以做為辨識惡性細胞的標籤，並適合成為癌症免疫治療的標靶。Globo H於人類醫學中已被廣泛研究，並發現它表現在多個不同的癌症，包含乳癌及肺癌，並被發現與這些惡性腫瘤中較差的預後具有顯著的相關性。執行在小鼠與人的免疫細胞中的分子實驗發現，globo H具有協助癌細胞迴避免疫系統偵測的功能，對於癌細胞的生長、血管新生、轉移，皆扮演要角。針對globo H抗原的疫苗在人乳癌患者的臨床試驗中發現，疫苗的副作用不明顯，並於部分出現globo H抗體力價上升的患者中可見存活時間上升的趨勢。犬隻至今未有與globo H相關之研究，因而本研究欲調查globo H於犬隻惡性乳腺腫瘤的表現狀況，並調查globo H是否與惡性乳腺腫瘤的負面預後因子具有相關性。在globo H陽性的犬隻中，我們也於第一期臨床試驗中測試globo H疫苗在犬隻中的安全性。 在49個惡性乳腺腫瘤樣本中檢測globo H表現，其中30（61%）個具陽性表現。與乳腺腫瘤預後因子比較，發現globo H的表現與臨床分期較早的案例具顯著相關性（P = 0.007），與大小較小的腫瘤具顯著的相關性（P = 0.04），並與病理惡性程度較低的腫瘤具顯著相關性（P = 0.001）。以上發現皆指向globo H陽性表現較常出現於預後較好的乳腺腫瘤，但無病存活時間和整體存活時間並未於統計上與globo H表現出現相關性。此研究結果發現globo H表現與犬隻乳腺腫瘤負面預後因子並無顯著相關性，與多篇人類腫瘤的研究結果牴觸。 五隻患有惡性乳腺腫瘤的犬隻參與globo H疫苗第一期臨床試驗，接受了globo H疫苗做為術後的輔助性治療。其中三隻犬隻於接受疫苗注射後出現了疫苗相關的副作用，最常見的副作用為精神沉鬱、厭食、及局部注射部位疼痛反應。副作用的嚴重程度大多輕微，僅有一隻犬隻因出現第三級的精神沉鬱而於後續治療中將疫苗注射的劑量減低，而所有的副作用皆為自限性的，都在三天內完全自行緩解。初步結果發現Globo H疫苗耐受度尚可。

Globo H, a tumor-associated carbohydrate antigen, is present on various epithelial tumors such as the breast, colon, ovarian, gastric, pancreatic, lung and prostate cancers in humans. It was realized that globo H had restricted presence on normal epithelial cells, making it an ideal target of immunotherapy. Preclinical studies showed that an antibody response could be successfully generated after vaccination of globo H conjugates. Phase II/III clinical trials found that human breast cancer patients with an elevated antibody response experienced prolonged progression free survival and overall survival times. The present study investigated globo H expression in canine malignant mammary gland tumors (MGT) and its prognostic significance in this type of cancer. Evidence of globo H facilitating cancer cells to evade immune surveillance was apparent in vitro, in addition to having associations with negative prognostic factors clinically in various cancers in humans, so we hypothesized that globo H expression would also have significant associations with the known negative prognostic factors in MGT. We also reported here the preliminary results from an accelerated phase I clinical trial of the globo H conjugate vaccine when used in dogs with malignant MGT. Globo H expression was evaluated in 49 malignant MGT samples from 45 dogs. Globo H was positive in 30 (61%) tumors and negative in 19 (39%) tumors. The median tumor size was significantly larger for globo H negative than positive tumors (P = 0.04). Globo H expression differed for early and advanced staged patients; globo H positive tumors were more likely to be early staged tumors (P = 0.007). Histologically, globo H expression was significantly more likely to be negative in grade 3 tumors than lower graded tumors (P = 0.001). Breed (P = 0.014) and weight (P = 0.013) also differed significantly for dogs with globo H positive and negative tumors. Globo H expression was not associated with overall survival time and disease-free interval for the dogs. Five dogs with malignant MGT received vaccinations of globo H-KLH with QS-21 as the post-operative adjuvant therapy. Four out of 5 dogs experienced various degrees of adverse events related to the vaccines. Two dogs experienced injection site reaction and 3 dogs became anorexic and lethargic after the second dose of vaccination. While most of the events were low grade and self-limiting, one dog experienced an episode of grade 3 lethargy after the second vaccination, requiring dose reductions in following vaccinations. Contrary to the findings from human studies, our results showed that globo H expression was associated with several favorable prognostic factors in MGT such as histologic low grade, early stage and small tumor size. According to the molecular functions of globo H, it is suspected that presence of globo H on well differentiated secretory epithelial cells may create a microenvironment suitable for tumor development, facilitating malignant transformation of mammary gland tumor cells. With highly malignant MGTs, tumor cells begin to lose their differentiation, hence the mostly undetectable globo H expression in grade 3 MGTs in our study. More research is required to clarify the discrepancy found in the present study and previous studies. Overall, the case number is too limited to conclude on adverse effects of globo H vaccine but when injected in the initial dose range, it was well tolerated. Further study on safety and efficacy of the vaccine should be continued.