Tumour-to-tumour metastasis: a rare case of prostate cancer metastasising to primary lung adenocarcinoma

Tumour-to-tumour metastasis (TTM) is a rare phenomenon that clinicians should be aware of when evaluating patients with a history of prostate cancer. We present the diagnosis and management of an 80-year-old former smoker with high-risk prostate cancer, who developed a lung nodule consistent with TTM. The patient had concurrent primary lung adenocarcinoma and metastatic prostate cancer, making this a unique case of dual primary and metastatic malignancies. The complexity of this case highlights the need for comprehensive evaluation and interdisciplinary management in patients with multiple malignancies. The literature review reveals that these are extremely rare occurrences, with most cases involving metastasis to the second primary tumour. Despite the challenges in diagnosing preoperatively, it is important to consider TTM as a possibility in patients with prostate cancer who present with a lung nodule. This report presents one of the few documented cases of TTM. It also reviews relevant cases in the literature and discusses the current situation in relation to established criteria for classifying combination tumours.