A case of raised CA 19-9 in a patient with desmoplastic fibroblastoma of the upper limb.

Carbohydrate antigen 19-9 (CA 19-9) is a tumor marker widely accepted as the most useful blood test in diagnosing and monitoring pancreatic cancer. However, CA 19-9 may also be raised in other conditions such as colorectal, hepatic, lung, and ovarian carcinoma as well as benign conditions such as hepatobiliary and pulmonary diseases. CA 19-9 is rarely elevated above 200 U/ml in benign conditions with values exceeding 1000 U/ml being highly suggestive of malignancy. The mechanism of secretion in both malignant and benign conditions remains unclear. Desmoplastic fibroblastoma (DF) is a benign soft tissue tumor. CA 19-9 has not been reported in association with DF previously. We present a case of raised serum CA 19-9 in a 71-year-old male attributed solely to DF in his left cubital fossa. The patient's CA 19-9 level rose from 56 U/ml at the time of presentation to 3763.8 U/ml over a period of 9 months. Post-DF excision, the CA 19-9 level decreased to 1464 U/ml at 1 month, 162.3 U/ml at 2.5 months, and 24U/ml, within normal range, at 7 months post-surgery. CA 19-9 levels continued to remain at 24 U/ml 1.5 years post-tumor excision. The CA 19-9 level in this patient was highly elevated which is unusual in association with a benign tumor. The rate of decrease in CA 19-9 level post-excision was in keeping with that reported after pancreatic cancer resections. This is the first case of DF in association with raised CA 19-9. © The Japan Society of Clinical Oncology 2021.