Background <p>Primary adenosquamous carcinoma of the prostate is an extremely rare and aggressive variant, accounting for less than 1% of all prostate cancers. Due to its rarity, the prognosis is poor, with no established treatment. Prostate-specific antigen levels are typically within the normal range in primary adenosquamous carcinoma of the prostate.</p> Case presentation <p>We present the case of a 57-year-old East Asian male in whom pathological and imaging findings led to the diagnosis of primary adenosquamous carcinoma of the prostate. His prostate-specific antigen levels were initially high and continued to increase rapidly thereafter to 161.89&#xa0;ng/ml. Although hormonal therapy achieved a reduction in prostate-specific antigen levels, the disease progressed rapidly, with extensive metastases to multiple sites, including the lung, lymph nodes, pancreas, bone, and skeletal muscle as an extremely rare metastatic site. The patient died 6 months after diagnosis despite subsequent multidisciplinary treatment.</p> Conclusion <p>This patient with primary adenosquamous carcinoma of the prostate demonstrated rapid increase of prostate-specific antigen as an uncommon clinical feature. Further accumulation of cases is needed to understand and treat this rare and aggressive disease.</p>