Fibroblast activation protein (FAP) is known to have prognostic significance in colorectal cancer (CRC). However, FAP and tertiary lymphoid structures (TLSs) have not been associated with each other in predicting the prognosis of CRC recurrence.

FAP expression was evaluated by real-time reverse transcription polymerase chain reaction in 195 CRC patients at Osaka International Cancer Institute (first data set). Immunohistochemistry (IHC) was then performed to stain FAP at the invasive margin (IM) and in the central tumour (CT) in 159 CRC patients at Osaka University Hospital (second data set). Consecutive slides were used to evaluate the presence of TLSs in 159 CRC patients from Osaka University Hospital.

The high FAP mRNA expression group (n=82) was associated with poor recurrence-free survival (RFS) compared with the low FAP expression group (n=83) (p=0.004). In the second data set, patients with high FAP expression in CT and TLS absence (n=49) showed significantly poorer RFS compared with those with low expression of FAP in CT and presence of TLSs (n=101) (p=0.002).

FAP in the CT combined with TLSs was shown to have significant prognostic value in predicting CRC recurrence after curative resection.