The importance of tumor size as a prognostic variable in cases of invasive carcinoma is robust enough to survivemeasurements derived variously from clinical estimates, mammograms, and gross and histologic sections. In many analyses it is second only to axillary node status as an independent prognostic factor. Tumor size is directly related to an increasing probability of regional metastasis, an increasing average number of involved axillary lymph nodes, and an increasing probability of recurrence and death.

The favorable prognosis of nonpalpable invasive carcinomas relative to palpable ones and of screening-detectedversus nonscreening-detected cancers is easily explained by their smaller size. In one report cancers 0.1 to 5 mm and 6 to 10 mm in diameter produced axillary metastasis in only 7.7 and 12.5 percent of cases, respectively.However, the incidence of positive nodes can range up to 21 percent for both of these size groups.15 Tumors of equal size are prognostically similar whether they are palpable or not and regardless of how they are detected.

The influence of primary tumor size on prognosis can be appreciated in both node-negative and node-positive cases. This relationship probably reflects increasing vascular and lymphatic dissemination with progressive tumor growth. Of particular interest are node-negative cases, where tumor size provides a readily available means foridentifying patients at low and high risk for recurrence.

Tumors 1.0 cm or less in diameter have an especially low risk of recurrence. The five-year disease-free survival of node-negative patients with tumors 1.0 cm or less in diameter is 92 to 96 percent. A large study at Memorial Sloan-Kettering Cancer Center found a 10-year relapse-free survival of 91 percent.

These and other studies support the contention that patients with the combination of node-negative disease and a tumor diameter of 1 cm or less represent a favorable subset of patients who would not benefit significantly from systemic adjuvant therapy.88 As failure rates are high enough in any case with macrometastasis to axillary lymphnodes to justify systemic adjuvant therapy, investigations have largely focused on the ability of other biologicvariables to further define the prognosis of node-negative individuals, a group that is increasing due to more widespread use of screening mammography.

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Traditional pathologic features (i.e., nodal status, tumor size, and tumor differentiation) continue to provide guides for prognosis and are information that is routinely available. ER and PR are also important, but are more important for guiding selection of hormone treatment than for determining prognosis. Newer prognostic indicators relating to the proliferative rates of tumors are increasingly available and are potentially helpful, but for the most part their role is uncertain.

ER and PR are the prime examples of prognostic indicators capable of identifying patients likely to respond to aparticular form of therapy (i.e., hormone therapy). Poor histologic grade may indicate a higher potential for response to chemotherapy. The overexpression of c-ERBB2 may be a potential indicator of resistance to chemotherapy and hormone therapy. It is possible that reliable markers for resistance or sensitivity to specific chemotherapeutic agents will be forthcoming, information that could have a constructive influence on treatment planning.

Patients with an excellent prognosis include women with DCIS and women with negative axillary nodes whose invasive carcinomas are less than 1.0 cm in diameter or who have special histologic types of carcinoma less than 3.0 cm in diameter. On the other hand, patients with any number of metastases to regional lymph nodes and node-negative patients with tumors more than 2.0 cm in maximum diameter have recurrence rates high enough to derive a substantial benefit from systemic therapy.

Node-negative patients with tumors 1.0 to 2.0 cm in diameter have an intermediate prognosis with average five-year disease-free survivals of about 85 percent. It is in this group that measures of proliferation such as histologic or nuclear grade, SPF, and ER status may have the most value in deciding for or against systemic therapy.