Although calcification seldom occurs in
pleomorphic adenoma, it often occurs in salivary glands, and so we decided to investigate the possible role of
calcium in this difference. A histochemical method using
glyoxal bis(2-hydroxyanil) demonstrated a small amount of
calcium outlining lumina and separated cells of epithelial structures and associated with cells of myxoid and chondroid regions in
pleomorphic adenoma, and a conspicuous amount in the acini of the associated salivary glands. A biochemical method using dry ashing demonstrated a significantly higher level of
calcium in the glands than in
pleomorphic adenoma. The results indicate that the
calcium is mainly associated with secretory granules, which are scarce in
pleomorphic adenoma, and with
proteoglycan present intercellularly and in stromal regions of
pleomorphic adenoma. The
calcium in secretory granules is of possible importance in calcification in lumina and epithelium, and that bound to
proteoglycan is possibly released following
necrosis to be of importance in stromal calcification. However, the overall low level of
calcium in
pleomorphic adenoma is the likely explanation for the usual lack of calcification.