Case Report: Genomic profiling in an invasive solid papillary carcinoma patient with liver metastasis and a history of invasive lobular carcinoma.

Solid papillary carcinoma (SPC) is a rare type of breast cancer that accounts for approximately 1% of all breast cancers. Although SPC is considered an indolent tumor, metastasis occurs in a few cases. The biological behavior and genomic characteristics of invasive SPC (ISPC) need to be further explored. A 44-year-old woman presented with a mass in her right breast in 2016 and ultrasound-guided mammotome (MMT) vacuum-assisted biopsy (VAB) pathology indicated an invasive lobular carcinoma (ILC). The patient subsequently underwent right partial mastectomy and axillary lymph node dissection, followed by radiotherapy and hormonal therapy. Eight years later, in 2024, ultrasonography revealed a 1.3 cm*1.0 cm mixed echogenic mass in her right breast, and biopsy pathology showed solid tumor nests with mucus secretion and thin fibrovascular cores. The pathological diagnosis was SPC with positive expression of the neuroendocrine marker synaptophysin (syn). The patient underwent right subcutaneous mastectomy with prosthesis implantation, followed by hormonal therapy. Four months later, multiple masses were found in her liver by ultrasonography and contrast-enhanced magnetic resonance imaging (MRI), which were eventually confirmed as metastatic SPC by pathology. A comprehensive next-generation sequencing (NGS) panel test was performed, and more genetic changes were identified including CCND1, FGF19, GATA3, KMT2C, MEN1, TP53, BRCA2, PI3KC3, and ERCC2::KLC3 fusion. The patient was treated with hormonal therapy combined with CDK4/6 inhibitors and so far no new lesions have appeared. We report a case of ISPC with liver metastasis in a patient with a history of ILC. Some meaningful genetic variations were identified by NGS. Further studies are needed to elucidate the molecular characteristics of SPC and explore the best therapeutic strategies.