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The goal of treatment with DCIS is prevention of local recurrence, with particular emphasis on the prevention of invasive breast cancer. Treatment decisions are largely based on information provided by mammography and, most especially, pathologic evaluation of the biopsy specimen. As such, in the consideration of treatment options it is important for the clinician to be aware of some of the technical limitations associated with the clinical and histopathologic assessment of DCIS.

Studies performed during the past two decades clearly have suggested that DCIS is not a single disease. Rather, this term encompasses a diverse group of lesions that differ with regard to their clinical presentation, mammographic features, extent and distribution within the breast, histologic characteristics, and biologic markers. Moreover, clinical follow-up studies have indicated that these lesions vary in their propensity to recur or progress to invasive breast cancer. As a consequence, a significant proportion of patients diagnosed with DCIS can be treated adequately with breast-conserving therapy (i.e., excision with or without radiation therapy). Which patients with DCIS can be treated safely with excision alone and which patients require radiation therapy after excision is a pressing clinical question. Attempts to resolve this issue have focused on the identification of risk factors for local recurrence after breast-conservation therapy for DCIS. With three exceptions (the prospectively randomized NSABP B-17, the EORTC 10853, and the United Kingdom Coordinating Committee on Cancer Research [UKCCCR] trials), all such studies have been retrospective in design. Nonetheless, a number of factors have been identified that may be important in defining local failure risk. These include symptomatic presentation (15,87,116), lesion size (108,116), histopathologic subtype (15), nuclear/cytologic grade (87,116,119), central necrosis (87,116,119), margin status (109,116,117), and patient age (15,42,117,127).

The relative importance of any histopathologic factor in predicting the probability of local recurrence and, in turn, selecting the appropriate therapeutic option for a given patient is unclear. This is partly the result of the inherent difficulty associated with the establishment of standardized and reproducible systems of pathologic classification, including such apparently straightforward assessments of grade, margin width, and lesion size.

Recent efforts to classify DCIS have been based primarily on the nuclear grade of the lesion and/or the presence or absence of necrosis. A number of studies have shown that there is an association between high nuclear grade and/or necrosis and the risk of local recurrence and progression to invasion (87,116,119). Although the criteria for histologic grading systems have been published, there are limited data regarding the ability of pathologists to apply them in a reproducible manner.

Several studies have shown that the status of the microscopic margins appears to be important in predicting the likelihood of recurrence in the breast for patients with both invasive breast cancer and DCIS treated with breast-conserving therapy (109,116,117). However, there are numerous technical problems in the evaluation of margins of breast-excision specimens. First, if a specimen is removed in more than one fragment, the margins cannot be evaluated. Second, there is no standardized method for sampling or reporting margins, and this process is subject to sampling error. Finally, it is often difficult to provide an accurate assessment of the margin width for patients who undergo a re-excision as the initial biopsy site can be eccentrically located in the surgical specimen.

Most DCIS lesions present as a nonpalpable, grossly inapparent mammographic abnormality, which can make accurate determination of the size or extent of the lesion difficult (Fig. 52.5). The two modalities available to assess the size of the lesion are mammography and pathologic examination. Mammography frequently will underestimate the pathologic extent of DCIS, particularly for well-differentiated lesions in which substantial areas of the tumor may not contain microcalcifications. Pathologic assessment of lesion size also can be difficult. Macroscopic examination of a specimen containing DCIS rarely reveals a grossly evident tumor that can be measured. Therefore, the assessment of the size of the lesion must be estimated from histologic sections.