Metastatic Patterns: Insights from Japanese Pathological Autopsy Registry Analysis.

Introduction: Understanding the metastatic patterns is crucial for the treatment of malignancies. This study aimed to identify the characteristic organ metastases of primary malignancies, including rare malignancies, and classify them according to their metastatic patterns.

Methods: We extracted data on primary malignancies and organ metastases from the Annual of Pathological Autopsy Cases in Japan recorded in 1993-2021. Autopsy findings of the primary and metastatic organs in patients with malignancy were recorded on an organ-by-organ basis. The metastatic frequency (number of metastases per autopsy) and the proportion (percentage of organs with metastases out of the total in a primary malignancy) for 48 organ metastasis sites across 76 primary malignancies were calculated. Metastatic patterns were classified into hierarchical and non-hierarchical clustering classifications based on the standard proportion of organ metastases.

Results: A total of 332,195 autopsy cases and 810,206 organ metastases were analyzed. The metastatic frequency of all malignancies was 2.44. Malignancies of the placenta, eye, and ovary showed a higher propensity for metastasis, whereas central nervous system malignancies showed a lower tendency. Metastasis site was a characteristic of each malignancy, with a particularly high proportion of lung metastasis in parathyroid malignancy and bone metastasis in prostate malignancy. In the hierarchical and non-hierarchical cluster methods, brain, lung, liver, bone, peritoneum, and hematolymphoid organ were key metastatic sites, and this factor divided primary malignancies into seven categories. The unweighted kappa coefficient comparing the two classification methods was 0.84 (95% confidence interval: 0.75-0.93). The proportion of metastatic organs was influenced by anatomical location and/or organ specificity of the primary malignancies.

Conclusion: Our study provides a comprehensive overview of the patterns and frequencies of metastatic organ sites associated with 76 primary malignancies. Our findings will provide useful information for future research and clinical practice.