ackerman

Small cell carcinomas that are morphologically analogous to their more common pulmonary counterpart and characterized by a very aggressive clinical course.

Mucinous (mucoid, gelatinous, colloid) carcinoma is characterized by prominent glandular formations and abundant mucin deposition, nearly all of which is extracellular (Figs 11.50 and
11.51). The mucin secreted by this tumor is a distinct O-acylated form of sialomucin which is immunoreactive for MUC2.546,550 The prognosis is better than that of signet ring carcinoma, but not significantly different from that of ordinary adenocarcinoma, except perhaps when the entire tumor is of mucinous type.

At the immunohistochemical level, the main mucin types expressed (with many variations and overlaps) are MUC1 for the intestinal type, MUC5AC for the diffuse type, MUC2 for the mucinous type, and MUC5B for the unclassified type (see below).430,435,448 There is also an interesting relationship between mucin type and tumor location, in the sense that MUC5AC is prevalent with carcinoma of the antrum whereas MUC2 is expressed in greater amounts with carcinoma of the cardia. CDX2 is present in about 90% of the cases, and HepPar-1 in approximately 80%.424 The former appears very early in tumor development, indicating a switch from a gastric to an intestinal phenotype.43

Signet ring carcinoma. This highly malignant neoplasm grows in a solid, acinar, or Indian file fashion and is composed primarily or exclusively of tumor cells with a signet ring configuration resulting from the intracellular accumulation of mucin.442,463,465,499 Ultrastructurally, the cells have intracytoplasmic lumina lined by microvilli.459 A
treacherous artifact closely mimicking signet ring cells may be seen in the stromal cells and lymphocytes present in the stroma of TUR specimens431 (see p. 1306).

Signet ring cell adenocarcinoma has been described as a primary uterine tumor.421 Before making this diagnosis, all attempts should be made to rule out the alternative possibilities of metastasis (particularly from breast and stomach) and of vacuolated decidual cells and stromal histiocytes simulating signet ring cells

Signet ring stromal tumor of the ovary is a very rare type but of great practical importance because of the fact that it can be easily mistaken for Krukenberg tumor. Some of the examples may be variants of sclerosing stromal tumor (see p. 1597). The tumor cells are negative for keratin, PAS, and mucin. Their behavior is benign.1104

Signet ring carcinoma. Signet ring carcinoma is a type of breast carcinoma in which a signifcant number of tumor cells show intracytoplasmic mucin accumulation, resulting in the typical signet ring appearance1007 (Fig. 20.97). Unfortunately, the term ‘signifcant’ is used differently by different people. Some will place a tumor into this category only if the majority of the cells have a signet ring morphology, whereas others would settle for a much smaller number.1004,1006 In any event, it is important to separate this tumor from mucinous carcinoma (in which the mucin is extracellular) because of their vastly different prognoses. Naturally, one should make room for exceptions. Occasionally the two types have been found to coexist (see p. 1700), and exceptionally the mucin of lobular carcinoma has been seen in an extracellular location

Immunohistochemically, signet ring carcinoma is positive for CK7 and MUC1, and usually negative for E-cadherin.