Rosen's Breast Pathology, 4e

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Unusual Clinical Presentation of Carcinoma

Pathology of the Occult Primary Carcinoma The primary tumor in more than 90% of cases is a form of usual IDC that is accompanied by intraductal carcinoma in most instances. 149,151 The histologic characteristics of the primary tumor and nodal metastases are similar (Fig. 33.12). A striking characteristic of many of the primary lesions, particularly tumors too small to be palpable, is a promi­ nent lymphocytic reaction in and around the lesion 133,138 (Figs. 33.13, 33.14, and 33.20). This is especially conspicuous when the primary ­lesion appeared to be largely or entirely in situ . An exceptionally high proportion of the occult primary duct carcinomas have apocrine cytology, and there is a ten­ dency for cytoplasmic clearing in the primary lesions as well as in the metastases (Figs. 33.12 and 33.13). The invasive car­ cinomas tend to be poorly differentiated histologically and cytologically. The data presented in Table 33.2 show some cases in which the only carcinoma detected in the breast appeared to be noninvasive. This phenomenon has been described in several studies. 131,140,167,169 It is thought that me­ tastases in these cases arose from invasive carcinoma that was inapparent with the light microscope amid the in situ FIG. 33.18.  Axillary nodal metastases that resemble intraductal carcinoma. All images are from cases of oc- cult carcinoma presenting as axillary nodal metastases.­ A: Round, “solid” aggregates of metastatic ductal car- cinoma. B: Necrosis and calcification in intraductal-like metastatic carcinoma. C: Metastatic apocrine cribriform carcinoma with peritumoral fibrosis that resembles a basement membrane.

lymph node obscured by metastatic tumor. Tissue around the tumor should be studied for evidence of axillary breast tissue. If found, this is presumptive evidence in support of an axillary primary, but it is necessary to find in situ car­ cinoma in conjunction with an invasive axillary lesion to establish a diagnosis of carcinoma arising in axillary breast tissue. Benign lesions that may be associated with ALNs, such as nevus cell aggregates and heterotopic glands, should not be misinterpreted as metastatic carcinoma. 166 For further in­ formation about heterotopic mammary tissue in ALNs and nodal nevus cell aggregates, see Chapter 43. ER and PR have been examined in axillary nodal me­ tastases from patients with occult carcinoma. 129,135,163,167,168 The largest series presented similar results, with 32% to 35% of nodal metastases positive for ER and PR, 24% to 27% positive for ER and negative for PR, and 38% to 44% negative for both receptors. 129,135 Others have also reported that ER and PR were negative in the majority of ALNs ana­ lyzed. 136 Lu et al. 151 reported that about one-third of the metastatic carcinomas were triple-negative. The presence of ER is highly suggestive of, but not specific for, mammary carcinoma.