Primary multiple cancers are spoken of as synchronous when two or more originate simultaneously (or at an interval of about six months), and as metachronous when there is a long interval (more than six months) between appearances. The distinction can be made with some degree of accuracy on surface, or accessible, cancers but hardly ever on deep-seated, visceral cancers, because the clinical manifestations of the latter do not usually coincide with the actual appearance of the growth. Some visceral cancers produce symptoms early; others remain silent until late, sometimes until they have attained considerable size. In the series reported here metachronicity could be reasonably accepted in one case only.
Some authors have included in the category of multiple cancers the condition in which a cancer appeared de novo long after the (surgical) cure of a previously existing cancer. This series contains a similar case (Case 6).
Perhaps of greater significance
FRIED BM. Primary Multiple Cancers. AMA Arch Surg. 1958;77(5):730-741. doi:10.1001/archsurg.1958.01290040078010