A 25-year-old woman was admitted for intermittent hematochezia. A digital rectal examination revealed a polyp 20 mm above the pectinate line. A full clinical investigation revealed no tumors elsewhere. A liquid-based cytology test combined with a human HPV-DNA test was performed to exclude cervical disease. The patient underwent a transanal resection, and the sessile rectal polyp (25 mm) was removed.
Histologically, a poorly differentiated submucosal tumor with relatively clear boundaries was discovered beneath the non-neoplastic rectal mucosa. The submucosal tumor showed a lymphoepithelioma-like growth pattern (Figure 1). The tumor was composed of sheets of large tumor cells with oval or round vesicular nuclei and prominent nucleoli, and had a syncytial cytoplasmic appearance. The intratumoral stroma was densely infiltrated with lymphocytes and plasma cells. The tumor invaded the submucosa to a depth of 11 mm, and the deep and radial margins were clear.
Immunohistochemically, the tumor cells were positive for pan-CK, P63, P40, and CK5/6 (Figure 2A), and negative for SATB2, Villin, CDX2, and CK20 (Figure 2B). Diffuse block-type immunoreactivity (diffuse nuclear and cytoplasmic staining) of p16 was shown (Figure 2C). Therefore, a diagnosis of poorly differentiated squamous carcinoma with lymphoepithelioma-like morphology was made.
Since LELCs have been previously reported to be closely related to EBV infection, in situ hybridization for EBV-encoded small RNA (EBER) was performed. The tumor cells were negative for EBER, while strongly positive staining was observed in the external positive control (Figure 2D). Linear array HPV genotyping (Yaneng Bio, Shenzhen, China) was performed for the detection of 23 HPV types, namely, 17 high-risk HPV types (16, 18, 31, 33, 35, 39, 45, 51-53, 56, 58, 59, 66, 68, 73, and 82) and 6 low-risk HPV types (6, 11, 42, 43, 81, and 83). High-risk HPV-16 was detected in this case. Therefore, this was a case of HPV-associated LELC of the anal canal.
Given that there was a strong local immune infiltration in the tumor microenvironment, immunostaining was performed for DNA mismatch repair (MMR) proteins, PD-L1, and CD8. The tumor showed intact nuclear staining of four MMR proteins (MLH1, PMS2, MSH2, and MSH6). Normal colonic mucosa (adjacent to the carcinoma) and lymphocytes served as positive internal controls. The immunostaining intensity of PD-L1 was evaluated by the combined positive score (CPS), and a strong immunoreaction was observed with a CPS > 70 (Figure 2E). We also analyzed the presence of intratumoral CD8+ T cells and found that abundant tumor-infiltrating lymphocytes (TILs) were CD8-positive (Figure 2F).
The patient subsequently underwent further endoscopic evaluation and mapping biopsies. Neither endoscopic nor microscopic examination revealed any abnormalities. Thereafter, the patient received three cycles of chemotherapy (paclitaxel + Cisplatin + capecitabine) combined with concurrent radiotherapy. The patient continued to be asymptomatic with no signs of recurrence or metastasis 8 months post-operation.